6a. 2. The Scapula (Shoulder Blade)

(Shoulder Blade)

The scapula forms the posterior part of the shoulder girdle. It is a flat, triangular bone, with two surfaces, three borders, and three angles.

Surfaces.—The costal or ventral surface (Fig. 202) presents a broad concavity, the subscapular fossa. The medial two-thirds of the fossa are marked by several oblique ridges, which run lateralward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the Subscapularis. The lateral third of the fossa is smooth and covered by the fibers of this muscle. The fossa is separated from the vertebral border by smooth triangular areas at the medial and inferior angles, and in the interval between these by a narrow ridge which is often deficient. These triangular areas and the intervening ridge afford attachment to the Serratus anterior. At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion. 2
The dorsal surface (Fig. 203) is arched from above downward, and is subdivided into two unequal parts by the spine; the portion above the spine is called the supraspinatous fossa, and that below it the infraspinatous fossa. 3
The supraspinatous fossa, the smaller of the two, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the Supraspinatus. 4
The infraspinatous fossa is much larger than the preceding; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part. The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle. 5
The dorsal surface is marked near the axillary border by an elevated ridge, which runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm. above the inferior angle. The ridge serves for the attachment of a fibrous septum, which separates the Infraspinatus from the Teres major and Teres minor. The surface between the ridge and the axillary border is narrow in the upper two-thirds of its extent, and is crossed near its center by a groove for the passage of the scapular circumflex vessels; it affords attachment to the Teres minor. Its lower third presents a broader, somewhat triangular surface, which gives origin to the Teres major, and over which the Latissimus dorsi glides; frequently the latter muscle takes origin by a few fibers from this part. The broad and narrow portions above alluded to are separated by an oblique line, which runs from the axillary border, downward and backward, to meet the elevated ridge: to it is attached a fibrous septum which separates the Teres muscles from each other. 6

The Spine (spina scapulæ).—The spine is a prominent plate of bone, which crosses obliquely the medial four-fifths of the dorsal surface of the scapula at its upper part, and separates the supra- from the infraspinatous fossa. It begins at the vertical border by a smooth, triangular area over which the tendon of insertion of the lower part of the Trapezius glides, and, gradually becoming more elevated, ends in the acromion, which overhangs the shoulder-joint. The spine is triangular, and flattened from above downward, its apex being directed toward the vertebral border. It presents two surfaces and three borders. Its superior surface is concave; it assits in forming the supraspinatous fossa, and gives origin to part of the Supraspinatus. Its inferior surface forms part of the infraspinatous fossa, gives origin to a portion of the Infraspinatus, and presents near its center the orifice of a nutrient canal. Of the three borders, the anterior is attached to the dorsal surface of the bone; the posterior, or crest of the spine, is broad, and presents two lips and an intervening rough interval. The Trapezius is attached to the superior lip, and a rough tubercle is generally seen on that portion of the spine which receives the tendon of insertion of the lower part of this muscle. The Deltoideus is attached to the whole length of the inferior lip. The interval between the lips is subcutaneous and partly covered by the tendinous fibers of these muscles. The lateral border, or base, the shortest of the three, is slightly concave; its edge, thick and round, is continuous above with the under surface of the acromion, below with the neck of the scapula. It forms the medial boundary of the great scapular notch, which serves to connect the supra- and infraspinatous fossæ. 7

The Acromion.—The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid cavity. Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the Deltoideus, and in the rest of its extent is subcutaneous. Its inferior surface is smooth and concave. Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the Deltoideus. Its medial border, shorter than the lateral, is concave, gives attachment to a portion of the Trapezius, and presents about its center a small, oval surface for articulation with the acromial end of the clavicle. 8

FIG. 202– Left scapula. Costal surface. (See enlarged image)

Its apex, which corresponds to the point of meeting of these two borders in front, is thin, and has attached to it the coracoacromial ligament. 9

FIG. 203– Left scapula. Dorsal surface. (See enlarged image)

Borders.—Of the three borders of the scapula, the superior is the shortest and thinnest; it is concave, and extends from the medial angle to the base of the coracoid process. At its lateral part is a deep, semicircular notch, the scapular notch, formed partly by the base of the coracoid process. This notch is converted into a foramen by the superior transverse ligament, and serves for the passage of the suprascapular nerve; sometimes the ligament is ossified. The adjacent part of the superior border affords attachment to the Omohyoideus. The axillary border is the thickest of the three. It begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and backward to the inferior angle. Immediately below the glenoid cavity is a rough impression, the infraglenoid tuberosity, about 2.5 cm. in length, which gives origin to the long head of the Triceps brachii; in front of this is a longitudinal groove, which extends as far as the lower third of this border, and affords origin to part of the Subscapularis. The inferior third is thin and sharp, and serves for the attachment of a few fibers of the Teres major behind, and of the Subscapularis in front. The vertebral border is the longest of the three, and extends from the medial to the inferior angle. It is arched, intermediate in thickness between the superior and the axillary borders, and the portion of it above the spine forms an obtuse angle with the part below. This border presents an anterior and a posterior lip, and an intermediate narrow area. The anterior lip affords attachment to the Serratus anterior; the posterior lip, to the Supraspinatus above the spine, the Infraspinatus below; the area between the two lips, to the Levator scapulæ above the triangular surface at the commencement of the spine, to the Rhomboideus minor on the edge of that surface, and to the Rhomboideus major below it; this last is attached by means of a fibrous arch, connected above to the lower part of the triangular surface at the base of the spine, and below to the lower part of the border. 10

FIG. 204– Posterior view of the thorax and shoulder girdle. (Morris.)

Angles.—Of the three angles, the medial, formed by the junction of the superior and vertebral borders, is thin, smooth, rounded, inclined somewhat lateralward, and gives attachment to a few fibers of the Levator scapulæ. The inferior angle, thick and rough, is formed by the union of the vertebral and axillary borders; its dorsal surface affords attachment to the Teres major and frequently to a few fibers of the Latissimus dorsi. The lateral angle is the thickest part of the bone, and is sometimes called the head of the scapula. On it is a shallow pyriform, articular surface, the glenoid cavity, which is directed lateralward and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest. The surface is covered with cartilage in the fresh state; and its margins, slightly raised, give attachment to a fibrocartilaginous structure, the glenoidal labrum, which deepens the cavity. At its apex is a slight elevation, the supraglenoid tuberosity, to which the long head of the Biceps brachii is attached. The neck of the scapula is the slightly constricted portion which surrounds the head; it is more distinct below and behind than above and in front.

The Coracoid Process (processus coracoideus).—The coracoid process is a thick curved process attached by a broad base to the upper part of the neck of the scapula; it runs at first upward and medialward; then, becoming smaller, it changes its direction, and projects forward and lateralward. The ascending portion, flattened from before backward, presents in front a smooth concave surface, across which the Subscapularis passes. The horizontal portion is flattened from above downward; its upper surface is convex and irregular, and gives attachment to the Pectoralis minor; its under surface is smooth; its medial and lateral borders are rough; the former gives attachment to the Pectoralis minor and the latter to the coracoacromial ligament; the apex is embraced by the conjoined tendon of origin of the Coracobrachialis and short head of the Biceps brachii and gives attachment to the coracoclavicular fascia. On the medial part of the root of the coracoid process is a rough impression for the attachment of the conoid ligament; and running from it obliquely forward and lateralward, on to the upper surface of the horizontal portion, is an elevated ridge for the attachment of the trapezoid ligament.

FIG. 205– Left scapula. Lateral view.

Structure.—The head, processes, and the thickened parts of the bone, contain cancellous tissue; the rest consists of a thin layer of compact tissue. The central part of the supraspinatous fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent muscles are separated only by fibrous tissue.

Ossification (Fig. 206).—The scapula is ossified from seven or more centers: one for the body, two for the coracoid process, two for the acromion, one for the vertebral border, and one for the inferior angle.

Ossification of the body begins about the second month of fetal life, by the formation of an irregular quadrilateral plate of bone, immediately behind the glenoid cavity. This plate extends so as to form the chief part of the bone, the spine growing up from its dorsal surface about the third month. At birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid process, the acromion, the vertebral border, and the inferior angle are cartilaginous. From the fifteenth to the eighteenth month after birth, ossification takes place in the middle of the coracoid process, which as a rule becomes joined with the rest of the bone about the fifteenth year. Between the fourteenth and twentieth years, ossification of the remaining parts takes place in quick succession, and usually in the following order; first, in the root of the coracoid process, in the form of a broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous part of the vertebral border; fourthly, near the extremity of the acromion; fifthly, in the vertebral border. The base of the acromion is formed by an extension from the spine; the two separate nuclei of the acromion unite, and then join with the extension from the spine. The upper third of the glenoid cavity is ossified from a separate center (subcoracoid), which makes its appearance between the tenth and eleventh years and joins between the sixteenth and the eighteenth. Further, an epiphysical plate appears for the lower part of the glenoid cavity, while the tip of the coracoid process frequently presents a separate nucleus. These various epiphyses are joined to the bone by the twenty-fifth year. Failure of bony union between the acromion and spine sometimes occurs, the junction being effected by fibrous tissue, or by an imperfect articulation; in some cases of supposed fracture of the acromion with ligamentous union, it is probable that the detached segment was never united to the rest of the bone.

FIG. 206– Plan of ossification of the scapula. From seven centers.

6a. 3. The Humerus

(Arm Bone)

The humerus (Figs. 207, 208) is the longest and largest bone of the upper extremity; it is divisible into a body and two extremities.

Upper Extremity.—The upper extremity consists of a large rounded head joined to the body by a constricted portion called the neck, and two eminences, the greater and lesser tubercles.

The Head (caput humeri).—The head, nearly hemispherical in form, 54 is directed upward, medialward, and a little backward, and articulates with the glenoid cavity of the scapula. The circumference of its articular surface is slightly constricted and is termed the anatomical neck, in contradistinction to a constriction below the tubercles called the surgical neck which is frequently the seat of fracture. Fracture of the anatomical neck rarely occurs.

The Anatomical Neck (collum anatomicum) is obliquely directed, forming an obtuse angle with the body. It is best marked in the lower half of its circumference; in the upper half it is represented by a narrow groove separating the head from the tubercles. It affords attachment to the articular capsule of the shoulder-joint, and is perforated by numerous vascular foramina.

The Greater Tubercle (tuberculum majus; greater tuberosity).—The greater tubercle is situated lateral to the head and lesser tubercle. Its upper surface is rounded and marked by three flat impressions: the highest of these gives insertion to the Supraspinatus; the middle to the Infraspinatus; the lowest one, and the body of the bone for about 2.5 cm. below it, to the Teres minor. The lateral surface of the greater tubercle is convex, rough, and continuous with the lateral surface of the body. 5

The Lesser Tubercle (tuberculum minus; lesser tuberosity).—The lesser tubercle, although smaller, is more prominent than the greater: it is situated in front, and is directed medialward and forward. Above and in front it presents an impression for the insertion of the tendon of the Subscapularis. 6
The tubercles are separated from each other by a deep groove, the intertubercular groove (bicipital groove), which lodges the long tendon of the Biceps brachii and transmits a branch of the anterior humeral circumflex artery to the shoulder-joint. It runs obliquely downward, and ends near the junction of the upper with the middle third of the bone. In the fresh state its upper part is covered with a thin layer of cartilage, lined by a prolongation of the synovial membrane of the shoulder-joint; its lower portion gives insertion to the tendon of the Latissimus dorsi. It is deep and narrow above, and becomes shallow and a little broader as it descends. Its lips are called, respectively, the crests of the greater and lesser tubercles (bicipital ridges), and form the upper parts of the anterior and medial borders of the body of the bone. 7

The Body or Shaft (corpus humeri).—The body is almost cylindrical in the upper half of its extent, prismatic and flattened below, and has three borders and three surfaces. 8

Borders.—The anterior border runs from the front of the greater tubercle above to the coronoid fossa below, separating the antero-medial from the antero-lateral surface. Its upper part is a prominent ridge, the crest of the greater tubercle; it serves for the insertion of the tendon of the Pectoralis major. About its center it forms the anterior boundary of the deltoid tuberosity; below, it is smooth and rounded, affording attachment to the Brachialis. 9
The lateral border runs from the back part of the greater tubercle to the lateral epicondyle, and separates the anterolateral from the posterior surface. Its upper half is rounded and indistinctly marked, serving for the attachment of the lower part of the insertion of the Teres minor, and below this giving origin to the lateral head of the Triceps brachii; its center is traversed by a broad but shallow oblique depression, the radial sulcus (musculospiral groove). Its lower part forms a prominent, rough margin, a little curved from behind forward, the lateral supracondylar ridge, which presents an anterior lip for the origin of the Brachioradialis above, and Extensor carpi radialis longus below, a posterior lip for the Triceps brachii, and an intermediate ridge for the attachment of the lateral intermuscular septum. 10

FIG. 207– Left humerus. Anterior view. (See enlarged image)

The medial border extends from the lesser tubercle to the medial epicondyle. Its upper third consists of a prominent ridge, the crest of the lesser tubercle, which gives insertion to the tendon of the Teres major. About its center is a slight impression for the insertion of the Coracobrachialis, and just below this is the entrance of the nutrient canal, directed downward; sometimes there is a second nutrient canal at the commencement of the radial sulcus. The inferior third of this border is raised into a slight ridge, the medial supracondylar ridge, which becomes very prominent below; it presents an anterior lip for the origins of the Brachialis and Pronator teres, a posterior lip for the medial head of the Triceps brachii, and an intermediate ridge for the attachment of the medial intermuscular septum. 11

Surfaces.—The antero-lateral surface is directed lateralward above, where it is smooth, rounded, and covered by the Deltoideus; forward and lateralward below, where it is slightly concave from above downward, and gives origin to part of the Brachialis. About the middle of this surface is a rough, triangular elevation, the deltoid tuberosity for the insertion of the Deltoideus; below this is the radial sulcus, directed obliquely from behind, forward, and downward, and transmitting the radial nerve and profunda artery. 12

FIG. 208– Left humerus. Posterior view. (See enlarged image)

The antero-medial surface, less extensive than the antero-lateral, is directed medialward above, forward and medialward below; its upper part is narrow, and forms the floor of the intertubercular groove which gives insertion to the tendon of the Latissimus dorsi; its middle part is slightly rough for the attachment of some of the fibers of the tendon of insertion of the Coracobrachialis; its lower part is smooth, concave from above downward, and gives origin to the Brachialis. 55 13
The posterior surface appears somewhat twisted, so that its upper part is directed a little medialward, its lower part backward and a little lateralward. Nearly the whole of this surface is covered by the lateral and medial heads of the Triceps brachii, the former arising above, the latter below the radial sulcus. 14

The Lower Extremity.—The lower extremity is flattened from before backward, and curved slightly forward; it ends below in a broad, articular surface, which is divided into two parts by a slight ridge. Projecting on either side are the lateral and medial epicondyles. The articular surface extends a little lower than the epicondyles, and is curved slightly forward; its medial extremity occupies a lower level than the lateral. The lateral portion of this surface consists of a smooth, rounded eminence, named the capitulum of the humerus; it articulates with the cupshaped depression on the head of the radius, and is limited to the front and lower part of the bone. On the medial side of this eminence is a shallow groove, in which is received the medial margin of the head of the radius. Above the front part of the capitulum is a slight depression, the radial fossa, which receives the anterior border of the head of the radius, when the forearm is flexed. The medial portion of the articular surface is named the trochlea, and presents a deep depression between two well-marked borders; it is convex from before backward, concave from side to side, and occupies the anterior, lower, and posterior parts of the extremity. The lateral border separates it from the groove which articulates with the margin of the head of the radius. The medial border is thicker, of greater length, and consequently more prominent, than the lateral. The grooved portion of the articular surface fits accurately within the semilunar notch of the ulna; it is broader and deeper on the posterior than on the anterior aspect of the bone, and is inclined obliquely downward and forward toward the medial side. Above the front part of the trochlea is a small depression, the coronoid fossa, which receives the coronoid process of the ulna during flexion of the forearm. Above the back part of the trochlea is a deep triangular depression, the olecranon fossa, in which the summit of the olecranon is received in extension of the forearm. These fossæ are separated from one another by a thin, transparent lamina of bone, which is sometimes perforated by a supratrochlear foramen; they are lined in the fresh state by the synovial membrane of the elbow-joint, and their margins afford attachment to the anterior and posterior ligaments of this articulation. The lateral epicondyle is a small, tuberculated eminence, curved a little forward, and giving attachment to the radial collateral ligament of the elbow-joint, and to a tendon common to the origin of the Supinator and some of the Extensor muscles. The medial epicondyle, larger and more prominent than the lateral, is directed a little backward; it gives attachment to the ulnar collateral ligament of the elbow-joint, to the Pronator teres, and to a common tendon of origin of some of the Flexor muscles of the forearm; the ulnar nerve runs in a groove on the back of this epicondyle. The epicondyles are continuous above with the supracondylar ridges. 15

Structure.—The extremities consist of cancellous tissue, covered with a thin, compact layer (Fig. 209); the body is composed of a cylinder of compact tissue, thicker at the center than toward the extremities, and contains a large medullary canal which extends along its whole length. 16

Ossification (Figs. 210, 211).—The humerus is ossified from eight centers, one for each of the following parts: the body, the head, the greater tubercle, the lesser tubercle, the capitulum, the trochlea, and one for each epicondyle. The center for the body appears near the middle of the bone in the eighth week of fetal life, and soon extends toward the extremities. At birth the humerus is ossified in nearly its whole length, only the extremities remaining cartilaginous. During the first year, sometimes before birth, ossification commences in the head of the bone, and during the third year the center for the greater tubercle, and during the fifth that for the lesser tubercle, make their appearance. By the sixth year the centers for the head and tubercles have joined, so as to form a single large epiphysis, which fuses with the body about the twentieth year. The lower end of the humerus is ossified as follows. At the end of the second year ossification begins in the capitulum, and extends medialward, to form the chief part of the articular end of the bone; the center for the medial part of the trochlea appears about the age of twelve. Ossification begins in the medial epicondyle about the fifth year, and in the lateral about the thirteenth or fourteenth year. About the sixteenth or seventeenth year, the lateral epicondyle and both portions of the articulating surface, having already joined, unite with the body, and at the eighteenth year the medial epicondyle becomes joined to it. 17

FIG. 209– Longitudinal section of head of left humerus. (See enlarged image)

FIG. 210– Plan of ossification of the humerus. (See enlarged image)

FIG. 211– Epiphysial lines of humerus in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue. (See enlarged image)

Note 54. Though the head is nearly hemispherical in form, its margin, as Humphry has shown, is by no means a true circle. Its greatest diameter is, from the top of the intertubercular groove in a direction downward, medialward, and backward. Hence it follows that the greatest elevation of the arm can be obtained by rolling the articular surface in this direction—that is to say, obliquely upward, lateralward, and forward. [back]
Note 55. A small, hook-shaped process of bone, the supracondylar process, varying from 2 to 20 mm. in length, is not infrequently found projecting from the antero-medial surface of the body of the humerus 5 cm. above the medial epicondyle. It is curved downward and forward, and its pointed end is connected to the medial border, just above the medial epicondyle, by a fibrous band, which gives origin to a portion of the Pronator teres; through the arch completed by this fibrous band the median nerve and brachial artery pass, when these structures deviate from their usual course. Sometimes the nerve alone is transmitted through it, or the nerve may be accompanied by the ulnar artery, in cases of high division of the brachial. A well-marked groove is usually found behind the process, in which the nerve and artery are lodged. This arch is the homologue of the supracondyloid foramen found in many animals, and probably serves in them to protect the nerve and artery from compression during the contraction of the muscles in this region. [back]

6a. 4. The Ulna

(Elbow Bone) 56

The ulna (Figs. 212, 213) is a long bone, prismatic in form, placed at the medial side of the forearm, parallel with the radius. It is divisible into a body and two extremities. Its upper extremity, of great thickness and strength, forms a large part of the elbow-joint; the bone diminishes in size from above downward, its lower extremity being very small, and excluded from the wrist-joint by the interposition of an articular disk.

The Upper Extremity (proximal extremity) (Fig. 212).—The upper extremity presents two curved processes, the olecranon and the coronoid process; and two concave, articular cavities, the semilunar and radial notches.

The Olecranon (olecranon process).—The olecranon is a large, thick, curved eminence, situated at the upper and back part of the ulna. It is bent forward at the summit so as to present a prominent lip which is received into the olecranon fossa of the humerus in extension of the forearm. Its base is contracted where it joins the body and the narrowest part of the upper end of the ulna. Its posterior surface, directed backward, is triangular, smooth, subcutaneous, and covered by a bursa. Its superior surface is of quadrilateral form, marked behind by a rough impression for the insertion of the Triceps brachii; and in front, near the margin, by a slight transverse groove for the attachment of part of the posterior ligament of the elbow-joint. Its anterior surface is smooth, concave, and forms the upper part of the semilunar notch. Its borders present continuations of the groove on the margin of the superior surface; they serve for the attachment of ligaments, viz., the back part of the ulnar collateral ligament medially, and the posterior ligament laterally. From the medial border a part of the Flexor carpi ulnaris arises; while to the lateral border the Anconæus is attached.

FIG. 212– Upper extremity of left ulna. Lateral aspect.

The Coronoid Process (processus coronoideus).—The coronoid process is a triangular eminence projecting forward from the upper and front part of the ulna. Its base is continuous with the body of the bone, and of considerable strength. Its apex is pointed, slightly curved upward, and in flexion of the forearm is received into the coronoid fossa of the humerus. Its upper surface is smooth, concave, and forms the lower part of the semilunar notch. Its antero-inferior surface is concave, and marked by a rough impression for the insertion of the Brachialis. At the junction of this surface with the front of the body is a rough eminence, the tuberosity of the ulna, which gives insertion to a part of the Brachialis; to the lateral border of this tuberosity the oblique cord is attached. Its lateral surface presents a narrow, oblong, articular depression, the radial notch. Its medial surface, by its prominent, free margin, serves for the attachment of part of the ulnar collateral ligament. At the front part of this surface is a small rounded eminence for the origin of one head of the Flexor digitorum sublimis; behind the eminence is a depression for part of the origin of the Flexor digitorum profundus; descending from the eminence is a ridge which gives origin to one head of the Pronator teres. Frequently, the Flexor pollicis longus arises from the lower part of the coronoid process by a rounded bundle of muscular fibers. 4

The Semilunar Notch (incisura semilunaris; greater sigmoid cavity).—The semilunar notch is a large depression, formed by the olecranon and the coronoid process, and serving for articulation with the trochlea of the humerus. About the middle of either side of this notch is an indentation, which contracts it somewhat, and indicates the junction of the olecranon and the coronoid process. The notch is concave from above downward, and divided into a medial and a lateral portion by a smooth ridge running from the summit of the olecranon to the tip of the coronoid process. The medial portion is the larger, and is slightly concave transversely; the lateral is convex above, slightly concave below. 5

The Radial Notch (incisura radialis; lesser sigmoid cavity).—The radial notch is a narrow, oblong, articular depression on the lateral side of the coronoid process; it receives the circumferential articular surface of the head of the radius. It is concave from before backward, and its prominent extremities serve for the attachment of the annular ligament. 6

The Body or Shaft (corpus ulnæ).—The body at its upper part is prismatic in form, and curved so as to be convex behind and lateralward; its central part is straight; its lower part is rounded, smooth, and bent a little lateralward. It tapers gradually from above downward, and has three borders and three surfaces. 7

Borders.—The volar border (margo volaris; anterior border) begins above at the prominent medial angle of the coronoid process, and ends below in front of the styloid process. Its upper part, well-defined, and its middle portion, smooth and rounded, give origin to the Flexor digitorum profundus; its lower fourth serves for the origin of the Pronator quadratus. This border separates the volar from the medial surface. 8
The dorsal border (margo dorsalis; posterior border) begins above at the apex of the triangular subcutaneous surface at the back part of the olecranon, and ends below at the back of the styloid process; it is well-marked in the upper three-fourths, and gives attachment to an aponeurosis which affords a common origin to the Flexor carpi ulnaris, the Extensor carpi ulnaris, and the Flexor digitorum profundus; its lower fourth is smooth and rounded. This border separates the medial from the dorsal surface. 9
The interosseous crest (crista interossea; external or interosseous border) begins above by the union of two lines, which converge from the extremities of the radial notch and enclose between them a triangular space for the origin of part of the Supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower fourth smooth and rounded. This crest gives attachment to the interosseous membrane, and separates the volar from the dorsal surface. 10

Surfaces.—The volar surface (facies volaris; anterior surface), much broader above than below, is concave in its upper three-fourths, and gives origin to the Flexor digitorum profundus; its lower fourth, also concave, is covered by the Pronator quadratus. The lower fourth is separated from the remaining portion by a ridge, directed obliquely downward and medialward, which marks the extent of origin of the Pronator quadratus. At the junction of the upper with the middle third of the bone is the nutrient canal, directed obliquely upward. 11

FIG. 213– Bones of left forearm. Anterior aspect. (See enlarged image)

FIG. 214– Bones of left forearm. Posterior aspect. (See enlarged image)

The dorsal surface (facies dorsalis; posterior surface) directed backward and lateralward, is broad and concave above; convex and somewhat narrower in the middle; narrow, smooth, and rounded below. On its upper part is an oblique ridge, which runs from the dorsal end of the radial notch, downward to the dorsal border; the triangular surface above this ridge receives the insertion of the Anconæus, while the upper part of the ridge affords attachment to the Supinator. Below this the surface is subdivided by a longitudinal ridge, sometimes called the perpendicular line, into two parts: the medial part is smooth, and covered by the Extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from above downward to the Supinator, the Abductor pollicis longus, the Extensor pollicis longus, and the Extensor indicis proprius. 12
The medial surface (facies medialis; internal surface) is broad and concave above, narrow and convex below. Its upper three-fourths give origin to the Flexor digitorum profundus; its lower fourth is subcutaneous. 13

FIG. 215– Plan of ossification of the ulna. From three centers. (See enlarged image)

FIG. 216– Epiphysial lines of ulna in a young adult. Lateral aspect. The lines of attachment of the articular capsules are in blue. (See enlarged image)

The Lower Extremity (distal extremity).—The lower extremity of the ulna is small, and presents two eminences; the lateral and larger is a rounded, articular eminence, termed the head of the ulna; the medial, narrower and more projecting, is a non-articular eminence, the styloid process. The head presents an articular surface, part of which, of an oval or semilunar form, is directed downward, and articulates with the upper surface of the triangular articular disk which separates it from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, and received into the ulnar notch of the radius. The styloid process projects from the medial and back part of the bone; it descends a little lower than the head, and its rounded end affords attachment to the ulnar collateral ligament of the wrist-joint. The head is separated from the styloid process by a depression for the attachment of the apex of the triangular articular disk, and behind, by a shallow groove for the tendon of the Extensor carpi ulnaris. 14

Structure.—The long, narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and dorsal surface. At the extremities the compact layer thins. The compact layer is continued onto the back of the olecranon as a plate of close spongy bone with lamellæ parallel. From the inner surface of this plate and the compact layer below it trabeculæ arch forward toward the olecranon and coronoid and cross other trabeculæ, passing backward over the medullary cavity from the upper part of the shaft below the coronoid. Below the coronoid process there is a small area of compact bone from which trabeculæ curve upward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of compact bone. The trabeculæ at the lower end have a more longitudinal direction. 15

Ossification (Figs. 215, 216).—The ulna is ossified from three centers: one each for the body, the inferior extremity, and the top of the olecranon. Ossification begins near the middle of the body, about the eighth week of fetal life, and soon extends through the greater part of the bone. At birth the ends are cartilaginous. About the fourth year, a center appears in the middle of the head, and soon extends into the styloid process. About the tenth year, a center appears in the olecranon near its extremity, the chief part of this process being formed by an upward extension of the body. The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year. 16

Articulations.—The ulna articulates with the humerus and radius. 17
Note 56. In the anatomical position, the forearm is placed in extension and supination with the palm looking forward and the thumb on the outer side. [back]

6a. 5. The Radius

The radius (Figs. 213, 214) is situated on the lateral side of the ulna, which exceeds it in length and size. Its upper end is small, and forms only a small part of the elbow-joint; but its lower end is large, and forms the chief part of the wrist-joint. It is a long bone, prismatic in form and slightly curved longitudinally. It has a body and two extremities.

The Upper Extremity (proximal extremity).—The upper extremity presents a head, neck, and tuberosity. The head is of a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna, narrow in the rest of its extent, which is embraced by the annular ligament. The head is supported on a round, smooth, and constricted portion called the neck, on the back of which is a slight ridge for the insertion of part of the Supinator. Beneath the neck, on the medial side, is an eminence, the radial tuberosity; its surface is divided into a posterior, rough portion, for the insertion of the tendon of the Biceps brachii, and an anterior, smooth portion, on which a bursa is interposed between the tendon and the bone.

The Body or Shaft (corpus radii).—The body is prismoid in form, narrower above than below, and slightly curved, so as to be convex lateralward. It presents three borders and three surfaces.

Borders.—The volar border (margo volaris; anterior border) extends from the lower part of the tuberosity above to the anterior part of the base of the styloid process below, and separates the volar from the lateral surface. Its upper third is prominent, and from its oblique direction has received the name of the oblique line of the radius; it gives origin to the Flexor digitorum sublimis and Flexor pollicis longus; the surface above the line gives insertion to part of the Supinator. The middle third of the volar border is indistinct and rounded. The lower fourth is prominent, and gives insertion to the Pronator quadratus, and attachment to the dorsal carpal ligament; it ends in a small tubercle, into which the tendon of the Brachioradialis is inserted.

The dorsal border (margo dorsalis; posterior border) begins above at the back of the neck, and ends below at the posterior part of the base of the styloid process; it separates the posterior from the lateral surface. It is indistinct above and below, but well-marked in the middle third of the bone.

The interosseous crest (crista interossea; internal or interosseous border) begins above, at the back part of the tuberosity, and its upper part is rounded and indistinct; it becomes sharp and prominent as it descends, and at its lower part divides into two ridges which are continued to the anterior and posterior margins of the ulnar notch. To the posterior of the two ridges the lower part of the interosseous membrane is attached, while the triangular surface between the ridges gives insertion to part of the Pronator quadratus. This crest separates the volar from the dorsal surface, and gives attachment to the interosseous membrane.

Surface.—The volar surface (facies volaris; anterior surface) is concave in its upper three-fourths, and gives origin to the Flexor pollicis longus; it is broad and flat in its lower fourth, and affords insertion to the Pronator quadratus. A prominent ridge limits the insertion of the Pronator quadratus below, and between this and the inferior border is a triangular rough surface for the attachment of the volar radiocarpal ligament. At the junction of the upper and middle thirds of the volar surface is the nutrient foramen, which is directed obliquely upward.

The dorsal surface (facies dorsalis; posterior surface) is convex, and smooth in the upper third of its extent, and covered by the Supinator. Its middle third is broad, slightly concave, and gives origin to the Abductor pollicis longus above, and the Extensor pollicis brevis below. Its lower third is broad, convex, and covered by the tendons of the muscles which subsequently run in the grooves on the lower end of the bone.

The lateral surface (facies lateralis; external surface) is convex throughout its entire extent. Its upper third gives insertion to the Supinator. About its center is a rough ridge, for the insertion of the Pronator teres. Its lower part is narrow, and covered by the tendons of the Abductor pollicis longus and Extensor pollicis brevis.

The Lower Extremity.—The lower extremity is large, of quadrilateral form, and provided with two articular surfaces—one below, for the carpus, and another at the medial side, for the ulna. The carpal articular surface is triangular, concave, smooth, and divided by a slight antero-posterior ridge into two parts. Of these, the lateral, triangular, articulates with the navicular bone; the medial, quadrilateral, with the lunate bone. The articular surface for the ulna is called the ulnar notch (sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna. These two articular surfaces are separated by a prominent ridge, to which the base of the triangular articular disk is attached; this disk separates the wrist-joint from the distal radioulnar articulation. This end of the bone has three non-articular surfaces—volar, dorsal, and lateral. The volar surface, rough and irregular, affords attachment to the volar radiocarpal ligament. The dorsal surface is convex, affords attachment to the dorsal radiocarpal ligament, and is marked by three grooves. Enumerated from the lateral side, the first groove is broad, but shallow, and subdivided into two by a slight ridge; the lateral of these two transmits the tendon of the Extensor carpi radialis longus, the medial the tendon of the Extensor carpi radialis brevis. The second is deep but narrow, and bounded laterally by a sharply defined ridge; it is directed obliquely from above downward and lateralward, and transmits the tendon of the Extensor pollicis longus. The third is broad, for the passage of the tendons of the Extensor indicis proprius and Extensor digitorum communis. The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the Brachioradialis, and by its apex to the radial collateral ligament of the wrist-joint. The lateral surface of this process is marked by a flat groove, for the tendons of the Abductor pollicis longus and Extensor pollicis brevis.

Structure.—The long narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and thinnest at the extremities except over the cup-shaped articular surface (fovea) of the head where it is thickened. The trabeculæ of the spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of the shaft to the fovea capituli; they are crossed by others parallel to the surface of the fovea. The arrangement at the lower end is somewhat similar. 11

Ossification (Figs. 217, 218).—The radius is ossified from three centers: one for the body, and one for either extremity. That for the body makes its appearance near the center of the bone, during the eighth week of fetal life. About the end of the second year, ossification commences in the lower end; and at the fifth year, in the upper end. The upper epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty. An additional center sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year. 12

FIG. 217– Plan of ossification of the radius. From three centers. (See enlarged image)

FIG. 218– Epiphysial lines of radius in a young adult. Anterior aspect. The line of attachment of the articular capsule of the wrist-joint is in blue. (See enlarged image)

6b. The Hand. 1. The Carpus

The skeleton of the hand (Figs. 219, 220) is subdivided into three segments: the carpus or wrist bones; the metacarpus or bones of the palm; and the phalanges or bones of the digits. 1

The Carpus (Ossa Carpi)

The carpal bones, eight in number, are arranged in two rows. Those of the proximal row, from the radial to the ulnar side, are named the navicular, lunate, triangular, and pisiform; those of the distal row, in the same order, are named the greater multangular, lesser multangular, capitate, and hamate. 2

Common Characteristics of the Carpal Bones.—Each bone (excepting the pisiform) presents six surfaces. Of these the volar or anterior and the dorsal or posterior surfaces are rough, for ligamentous attachment; the dorsal surfaces being the broader, except in the navicular and lunate. The superior or proximal, and inferior or distal surfaces are articular, the superior generally convex, the inferior concave; the medial and lateral surfaces are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated. The structure in all is similar, viz., cancellous tissue enclosed in a layer of compact bone. 3

Bones of the Proximal Row (upper row).—The Navicular Bone (os naviculare manus; scaphoid bone) (Fig. 221).—The navicular bone is the largest bone of the proximal row, and has received its name from its fancied resemblance to a boat. It is situated at the radial side of the carpus, its long axis being from above downward, lateralward, and forward. The superior surface is convex, smooth, of triangular shape, and articulates with the lower end of the radius. The inferior surface, directed downward, lateralward, and backward, is also smooth, convex, and triangular, and is divided by a slight ridge into two parts, the lateral articulating with the greater multangular, the medial with the lesser multangular. On the dorsal surface is a narrow, rough groove, which runs the entire length of the bone, and serves for the attachment of ligaments. The volar surface is concave above, and elevated at its lower and lateral part into a rounded projection, the tubercle, which is directed forward and gives attachment to the transverse carpal ligament and sometimes origin to a few fibers of the Abductor pollicis brevis. The lateral surface is rough and narrow, and gives attachment to the radial collateral ligament of the wrist. The medial surface presents two articular facets; of these, the superior or smaller is flattened of semilunar form, and articulates with the lunate bone; the inferior or larger is concave, forming with the lunate a concavity for the head of the capitate bone. 4

FIG. 219– Bones of the left hand. Volar surface. (See enlarged image)

FIG. 220– Bones of the left hand. Dorsal surface. (See enlarged image)

Articulations.—The navicular articulates with five bones: the radius proximally, greater and lesser multangulars distally, and capitate and lunate medially. 5

The Lunate Bone (os lunatum; semilunar bone) (Fig. 222).—The lunate bone may be distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row of the carpus, between the navicular and triangular. The superior surface, convex and smooth, articulates with the radius. The inferior surface is deeply concave, and of greater extent from before backward than transversely: it articulates with the head of the capitate, and, by a long, narrow facet (separated by a ridge from the general surface), with the hamate. The dorsal and volar surfaces are rough, for the attachment of ligaments, the former being the broader, and of a somewhat rounded form. The lateral surface presents a narrow, flattened, semilunar facet for articulation with the navicular. The medial surface is marked by a smooth, quadrilateral facet, for articulation with the triangular. 6

FIG. 221– The left navicular bone. (See enlarged image)

FIG. 222– The left lunate bone. (See enlarged image)

Articulations.—The lunate articulates with five bones: the radius proximally, capitate and hamate distally, navicular laterally, and triangular medially. 7

FIG. 223– The left triangular bone. (See enlarged image)

FIG. 224– The left pisiform bone. (See enlarged image)

The Triangular Bone (os triquetum; cuneiform bone) (Fig. 223).—The triangular bone may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone. It is situated at the upper and ulnar side of the carpus. The superior surface presents a medial, rough, non-articular portion, and a lateral convex articular portion which articulates with the triangular articular disk of the wrist. The inferior surface, directed lateralward, is concave, sinuously curved, and smooth for articulation with the hamate. The dorsal surface is rough for the attachment of ligaments. The volar surface presents, on its medial part, an oval facet, for articulation with the pisiform; its lateral part is rough for ligamentous attachment. The lateral surface, the base of the pyramid, is marked by a flat, quadrilateral facet, for articulation with the lunate. The medial surface, the summit of the pyramid, is pointed and roughened, for the attachment of the ulnar collateral ligament of the wrist. 8

Articulations.—The triangular articulates with three bones: the lunate laterally, the pisiform in front, the hamate distally; and with the triangular articular disk which separates it from the lower end of the ulna. 9

The Pisiform Bone (os pisiforme) (Fig. 224).—The pisiform bone may be known by its small size, and by its presenting a single articular facet. It is situated on a plane anterior to the other carpal bones and is spheroidal in form. Its dorsal surface presents a smooth, oval facet, for articulation with the triangular: this facet approaches the superior, but not the inferior border of the bone. The volar surface is rounded and rough, and gives attachment to the transverse carpal ligament, and to the Flexor carpi ulnaris and Abductor digiti quinti. The lateral and medial surfaces are also rough, the former being concave, the latter usually convex. 10

Articulation.—The pisiform articulates with one bone, the triangular. 11

Bones of the Distal Row (lower row).—The Greater Multangular Bone (os multangulum majus; trapezium) (Fig. 225).—The greater multangular bone may be distinguished by a deep groove on its volar surface. It is situated at the radial side of the carpus, between the navicular and the first metacarpal bone. The superior surface is directed upward and medialward; medially it is smooth, and articulates with the navicular; laterally it is rough and continuous with the lateral surface. The inferior surface is oval, concave from side to side, convex from before backward, so as to form a saddle-shaped surface for articulation with the base of the first metacarpal bone. The dorsal surface is rough. The volar surface is narrow and rough. At its upper part is a deep groove, running from above obliquely downward and medialward; it transmits the tendon of the Flexor carpi radialis, and is bounded laterally by an oblique ridge. This surface gives origin to the Opponens pollicis and to the Abductor and Flexor pollicis brevis; it also affords attachment to the transverse carpal ligament. The lateral surface is broad and rough, for the attachment of ligaments. The medial surface presents two facets; the upper, large and concave, articulates with the lesser multangular; the lower, small and oval, with the base of the second metacarpal. 12

FIG. 225– The left greater multangular bone. (See enlarged image)

Articulations.—The greater multangular articulates with four bones: the navicular proximally, the first metacarpal distally, and the lesser multangular and second metacarpal medially. 13

The Lesser Multangular Bone (os multangulum minus; trapezoid bone) (Fig. 226).—The lesser multangular is the smallest bone in the distal row. It may be known by its wedge-shaped form, the broad end of the wedge constituting the dorsal, the narrow end the volar surface; and by its having four articular facets touching each other, and separated by sharp edges. The superior surface, quadrilateral, smooth, and slightly concave, articulates with the navicular. The inferior surface articulates with the proximal end of the second metacarpal bone; it is convex from side to side, concave from before backward and subdivided by an elevated ridge into two unequal facets. The dorsal and volar surfaces are rough for the attachment of ligaments, the former being the larger of the two. The lateral surface, convex and smooth, articulates with the greater multangular. The medial surface is concave and smooth in front, for articulation with the capitate; rough behind, for the attachment of an interosseous ligament. 14

FIG. 226– The left lesser multangular bone. (See enlarged image)

Articulations.—The lesser multangular articulates with four bones: the navicular proximally, second metacarpal distally, greater multangular laterally, and capitate medially. 15

The Capitate Bone (os capitatum; os magnum) (Fig. 227).—The capitate bone is the largest of the carpal bones, and occupies the center of the wrist. It presents, above, a rounded portion or head, which is received into the concavity formed by the navicular and lunate; a constricted portion or neck; and below this, the body. The superior surface is round, smooth, and articulates with the lunate. The inferior surface is divided by two ridges into three facets, for articulation with the second, third, and fourth metacarpal bones, that for the third being the largest. The dorsal surface is broad and rough. The volar surface is narrow, rounded, and rough, for the attachment of ligaments and a part of the Adductor pollicis obliquus. 16

FIG. 227– The left capitate bone. (See enlarged image)

FIG. 228– The left hamate bone. (See enlarged image)

The lateral surface articulates with the lesser multangular by a small facet at its anterior inferior angle, behind which is a rough depression for the attachment of an interosseous ligament. Above this is a deep, rough groove, forming part of the neck, and serving for the attachment of ligaments; it is bounded superiorly by a smooth, convex surface, for articulation with the navicular. The medial surface articulates with the hamate by a smooth, concave, oblong facet, which occupies its posterior and superior parts; it is rough in front, for the attachment of an interosseous ligament. 17

Articulations.—The capitate articulates with seven bones: the navicular and lunate proximally, the second, third, and fourth metacarpals distally, the lesser multangular on the radial side, and the hamate on the ulnar side. 18

The Hamate Bone (os hamatum; unciform bone) (Fig. 228).—The hamate bone may be readily distinguished by its wedge-shaped form, and the hook-like process which projects from its volar surface. It is situated at the medial and lower angle of the carpus, with its base downward, resting on the fourth and fifth metacarpal bones, and its apex directed upward and lateralward. The superior surface, the apex of the wedge, is narrow, convex, smooth, and articulates with the lunate. The inferior surface articulates with the fourth and fifth metacarpal bones, by concave facets which are separated by a ridge. The dorsal surface is triangular and rough for ligamentous attachment. The volar surface presents, at its lower and ulnar side, a curved, hook-like process, the hamulus, directed forward and lateralward. This process gives attachment, by its apex, to the transverse carpal ligament and the Flexor carpi ulnaris; by its medial surface to the Flexor brevis and Opponens digiti quinti; its lateral side is grooved for the passage of the Flexor tendons into the palm of the hand. It is one of the four eminences on the front of the carpus to which the transverse carpal ligament of the wrist is attached; the others being the pisiform medially, the oblique ridge of the greater multangular and the tubercle of the navicular laterally. The medial surface articulates with the triangular bone by an oblong facet, cut obliquely from above, downward and medialward. The lateral surface articulates with the capitate by its upper and posterior part, the remaining portion being rough, for the attachment of ligaments. 19

Articulations.—The hamate articulates with five bones: the lunate proximally, the fourth and fifth metacarpals distally, the triangular medially, the capitate laterally. 20

6b. 2. The Metacarpus

The metacarpus consists of five cylindrical bones which are numbered from the lateral side (ossa metacarpalia I-V); each consists of a body and two extremities.

Common Characteristics of the Metacarpal Bones.—The Body (corpus; shaft).—The body is prismoid in form, and curved, so as to be convex in the longitudinal direction behind, concave in front. It presents three surfaces: medial, lateral, and dorsal. The medial and lateral surfaces are concave, for the attachment of the Interossei, and separated from one another by a prominent anterior ridge. The dorsal surface presents in its distal two-thirds a smooth, triangular, flattened area which is covered in the fresh state, by the tendons of the Extensor muscles. This surface is bounded by two lines, which commence in small tubercles situated on either side of the digital extremity, and, passing upward, converge and meet some distance above the center of the bone and form a ridge which runs along the rest of the dorsal surface to the carpal extremity. This ridge separates two sloping surfaces for the attachment of the Interossei dorsales. To the tubercles on the digital extremities are attached the collateral ligaments of the metacarpophalangeal joints.

The Base or Carpal Extremity (basis) is of a cuboidal form, and broader behind than in front: it articulates with the carpus, and with the adjoining metacarpal bones; its dorsal and volar surfaces are rough, for the attachment of ligaments.

The Head or Digital Extremity (capitulum) presents an oblong surface markedly convex from before backward, less so transversely, and flattened from side to side; it articulates with the proximal phalanx. It is broader, and extends farther upward, on the volar than on the dorsal aspect, and is longer in the antero-posterior than in the transverse diameter. On either side of the head is a tubercle for the attachment of the collateral ligament of the metacarpophalangeal joint. The dorsal surface, broad and flat, supports the Extensor tendons; the volar surface is grooved in the middle line for the passage of the Flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface.

Characteristics of the Individual Metacarpal Bones.—The First Metacarpal Bone (os metacarpale I; metacarpal bone of the thumb) (Fig. 229) is shorter and stouter than the others, diverges to a greater degree from the carpus, and its volar surface is directed toward the palm. The body is flattened and broad on its dorsal surface, and does not present the ridge which is found on the other metacarpal bones; its volar surface is concave from above downward. On its radial border is inserted the Opponens pollicis; its ulnar border gives origin to the lateral head of the first Interosseus dorsalis. The base presents a concavo-convex surface, for articulation with the greater multangular; it has no facets on its sides, but on its radial side is a tubercle for the insertion of the Abductor pollicis longus. The head is less convex than those of the other metacarpal bones, and is broader from side to side than from before backward. On its volar surface are two articular eminences, of which the lateral is the larger, for the two sesamoid bones in the tendons of the Flexor pollicis brevis.

FIG. 229– The first metacarpal. (Left.) (See enlarged image)

The Second Metacarpal Bone (os metacarpale II; metacarpal bone of the index finger) (Fig. 230) is the longest, and its base the largest, of the four remaining bones. Its base is prolonged upward and medialward, forming a prominent ridge. It presents four articular facets: three on the upper surface and one on the ulnar side. Of the facets on the upper surface the intermediate is the largest and is concave from side to side, convex from before backward for articulation with the lesser multangular; the lateral is small, flat and oval for articulation with the greater multangular; the medial, on the summit of the ridge, is long and narrow for articulation with the capitate. The facet on the ulnar side articulates with the third metacarpal. The Extensor carpi radialis longus is inserted on the dorsal surface and the Flexor carpi radialis on the volar surface of the base. 6
The Third Metacarpal Bone (os metacarpale III; metacarpal bone of the middle finger) (Fig. 231) is a little smaller than the second. The dorsal aspect of its base presents on its radial side a pyramidal eminence, the styloid process, which extends upward behind the capitate; immediately distal to this is a rough surface for the attachment of the Extensor carpi radialis brevis. The carpal articular facet is concave behind, flat in front, and articulates with the capitate. On the radial side is a smooth, concave facet for articulation with the second metacarpal, and on the ulnar side two small oval facets for the fourth metacarpal. 7
The Fourth Metacarpal Bone (os metacarpale IV; metacarpal bone of the ring finger) (Fig. 232) is shorter and smaller than the third. The base is small and quadrilateral; its superior surface presents two facets, a large one medially for articulation with the hamate, and a small one laterally for the capitate. On the radial side are two oval facets, for articulation with the third metacarpal; and on the ulnar side a single concave facet, for the fifth metacarpal. 8
The Fifth Metacarpal Bone (os metacarpale V; metacarpal bone of the little finger) (Fig. 233) presents on its base one facet on its superior surface, which is concavo-convex and articulates with the hamate, and one on its radial side, which articulates with the fourth metacarpal. On its ulnar side is a prominent tubercle for the insertion of the tendon of the Extensor carpi ulnaris. The dorsal surface of the body is divided by an oblique ridge, which extends from near the ulnar side of the base to the radial side of the head. The lateral part of this surface serves for the attachment of the fourth Interosseus dorsalis; the medial part is smooth, triangular, and covered by the Extensor tendons of the little finger. 9

FIG. 230– The second metacarpal. (Left.) (See enlarged image)

FIG. 231– The third metacarpal. (Left.) (See enlarged image)

FIG. 232– The fourth metacarpal. (Left.) (See enlarged image)

FIG. 233– The fifth metacarpal. (Left.) (See enlarged image)

Articulations.—Besides their phalangeal articulations, the metacarpal bones articulate as follows: the first with the greater multangular; the second with the greater multangular, lesser multangular, capitate and third metacarpal; the third with the capitate and second and fourth metacarpals; the fourth with the capitate, hamate, and third and fifth metacarpals; and the fifth with the hamate and fourth metacarpal. 10

6b. 3. The Phalanges of the Hand

(Phalanges Digitorum Manus)

The phalanges are fourteen in number, three for each finger, and two for the thumb. Each consists of a body and two extremities. The body tapers from above downward, is convex posteriorly, concave in front from above downward, flat from side to side; its sides are marked by rough which give attachment to the fibrous sheaths of the Flexor tendons. The proximal extremities of the bones of the first row present oval, concave articular surfaces, broader from side to side than from before backward. The proximal extremity of each of the bones of the second and third rows presents a double concavity separated by a median ridge. The distal extremities are smaller than the proximal, and each ends in two condyles separated by a shallow groove; the articular surface extends farther on the volar than on the dorsal surface, a condition best marked in the bones of the first row. 1
The ungual phalanges are convex on their dorsal and flat on their volar surfaces; they are recognized by their small size, and by a roughened, elevated surface of a horseshoe form on the volar surface of the distal extremity of each which serves to support the sensitive pulp of the finger.

FIG. 234– Plan of ossification of the hand. (See enlarged image)

Articulations.—In the four fingers the phalanges of the first row articulate with those of the second row and with the metacarpals; the phalanges of the second row with those of the first and third rows, and the ungual phalanges with those of the second row. In the thumb, which has only two phalanges, the first phalanx articulates by its proximal extremity with the metacarpal bone and by its distal with the ungual phalanx.

Ossification of the Bones of the Hand.—The carpal bones are each ossified from a single center, and ossification proceeds in the following order (Fig. 234): in the capitate and hamate, during the first year, the former preceding the latter; in the triangular, during the third year; in the lunate and greater multangular, during the fifth year, the former preceding the latter; in the navicular, during the sixth year; in the lesser multangular, during the eighth year; and in the pisiform, about the twelfth year 4
Occasionally an additional bone, the os centrale, is found on the back of the carpus, lying between the navicular, lesser multangular, and capitate. During the second month of fetal life it is represented by a small cartilaginous nodule, which usually fuses with the cartilaginous navicular. Sometimes the styloid process of the third metacarpal is detached and forms an additional ossicle.

The metacarpal bones are each ossified from two centers: one for the body and one for the distal extremity of each of the second, third, fourth, and fifth bones; one for the body and one for the base of the first metacarpal bone. 57 The first metacarpal bone is therefore ossified in the same manner as the phalanges, and this has led some anatomists to regard the thumb as being made up of three phalanges, and not of a metacarpal bone and two phalanges. Ossification commences in the middle of the body about the eighth or ninth week of fetal life, the centers for the second and third metacarpals being the first, and that for the first metacarpal, the last, to appear; about the third year the distal extremities of the metacarpals of the fingers, and the base of the metacarpal of the thumb, begin to ossify; they unite with the bodies about the twentieth year.

The phalanges are each ossified from two centers: one for the body, and one for the proximal extremity. Ossification begins in the body, about the eighth week of fetal life. Ossification of the proximal extremity commences in the bones of the first row between the third and fourth years, and a year later in those of the second and third rows. The two centers become united in each row between the eighteenth and twentieth years.

In the ungual phalanges the centers for the bodies appear at the distal extremities of the phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all the bones of the hand, the ungual phalanges are the first to ossify. 8
Note 57. Allen Thomson demonstrated the fact that the first metacarpal bone is often developed from three centers: that is to say, there is a separate nucleus for the distal end, forming a distinct epiphysis visible at the age of seven or eight years. He also stated that there are traces of a proximal epiphysis in the second metacarpal bone, Journal of Anatomy and Physiology, 1869. [back]

6c. The Bones of the Lower Extremity. 1. The Hip Bone

(Ossa Extremitatis Inferioris) & (Os Coxæ; Innominate Bone)

The hip bone is a large, flattened, irregularly shaped bone, constricted in the center and expanded above and below. It meets its fellow on the opposite side in the middle line in front, and together they form the sides and anterior wall of the pelvic cavity. It consists of three parts, the ilium, ischium, and pubis, which are distinct from each other in the young subject, but are fused in the adult; the union of the three parts takes place in and around a large cup-shaped articular cavity, the acetabulum, which is situated near the middle of the outer surface of the bone. The ilium, so-called because it supports the flank, is the superior broad and expanded portion which extends upward from the acetabulum. The ischium is the lowest and strongest portion of the bone; it proceeds downward from the acetabulum, expands into a large tuberosity, and then, curving forward, forms, with the pubis, a large aperture, the obturator foramen. The pubis extends medialward and downward from the acetabulum and articulates in the middle line with the bone of the opposite side: it forms the front of the pelvis and supports the external organs of generation.

The Ilium (os ilii).—The ilium is divisible into two parts, the body and the ala; the separation is indicated on the internal surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum.

The Body (corpus oss. ilii).—The body enters into the formation of the acetabulum, of which it forms rather less than two-fifths. Its external surface is partly articular, partly non-articular; the articular segment forms part of the lunate surface of the acetabulum, the non-articular portion contributes to the acetabular fossa. The internal surface of the body is part of the wall of the lesser pelvis and gives origin to some fibers of the Obturator internus. Below, it is continuous with the pelvic surfaces of the ischium and pubis, only a faint line indicating the place of union. 3

FIG. 235– Right hip bone. External surface. (See enlarged image)

The Ala (ala oss. ilii).—The ala is the large expanded portion which bounds the greater pelvis laterally. It presents for examination two surfaces—an external and an internal—a crest, and two borders—an anterior and a posterior. The external surface (Fig. 235), known as the dorsum ilii, is directed backward and lateralward behind, and downward and lateralward in front. It is smooth, convex in front, deeply concave behind; bounded above by the crest, below by the upper border of the acetabulum, in front and behind by the anterior and posterior borders. This surface is crossed in an arched direction by three lines—the posterior, anterior, and inferior gluteal lines. The posterior gluteal line (superior curved line), the shortest of the three, begins at the crest, about 5 cm. in front of its posterior extremity; it is at first distinctly marked, but as it passes downward to the upper part of the greater sciatic notch, where it ends, it becomes less distinct, and is often altogether lost. Behind this line is a narrow semilunar surface, the upper part of which is rough and gives origin to a portion of the Glutæus maximus; the lower part is smooth and has no muscular fibers attached to it. The anterior gluteal line (middle curved line), the longest of the three, begins at the crest, about 4 cm. behind its anterior extremity, and, taking a curved direction downward and backward, ends at the upper part of the greater sciatic notch. The space between the anterior and posterior gluteal lines and the crest is concave, and gives origin to the Glutæus medius. Near the middle of this line a nutrient foramen is often seen. The inferior gluteal line (inferior curved line), the least distinct of the three, begins in front at the notch on the anterior border, and, curving backward and downward, ends near the middle of the greater sciatic notch. The surface of bone included between the anterior and inferior gluteal lines is concave from above downward, convex from before backward, and gives origin to the Glutæus minimus. Between the inferior gluteal line and the upper part of the acetabulum is a rough, shallow groove, from which the reflected tendon of the Rectus femoris arises. 4

FIG. 236– Right hip bone. Internal surface. (See enlarged image)

The internal surface (Fig. 236) of the ala is bounded above by the crest, below, by the arcuate line; in front and behind, by the anterior and posterior borders. It presents a large, smooth, concave surface, called the iliac fossa, which gives origin to the Iliacus and is perforated at its inner part by a nutrient canal; and below this a smooth, rounded border, the arcuate line, which runs downward, forward, and medialward. Behind the iliac fossa is a rough surface, divided into two portions, an anterior and a posterior. The anterior surface (auricular surface), so called from its resemblance in shape to the ear, is coated with cartilage in the fresh state, and articulates with a similar surface on the side of the sacrum. The posterior portion, known as the iliac tuberosity, is elevated and rough, for the attachment of the posterior sacroiliac ligaments and for the origins of the Sacrospinalis and Multifidus. Below and in front of the auricular surface is the preauricular sulcus, more commonly present and better marked in the female than in the male; to it is attached the pelvic portion of the anterior sacroiliac ligament. 5
The crest of the ilium is convex in its general outline but is sinuously curved, being concave inward in front, concave outward behind. It is thinner at the center than at the extremities, and ends in the anterior and posterior superior iliac spines. The surface of the crest is broad, and divided into external and internal lips, and an intermediate line. About 5 cm. behind the anterior superior iliac spine there is a prominent tubercle on the outer lip. To the external lip are attached the Tensor fasciæ latæ, Obliquus externus abdominis, and Latissimus dorsi, and along its whole length the fascia lata; to the intermediate line the Obliquus internus abdominis; to the internal lip, the fascia iliaca, the Transversus abdominis, Quadratus lumborum, Sacrospinalis, and Iliacus. 6
The anterior border of the ala is concave. It presents two projections, separated by a notch. Of these, the uppermost, situated at the junction of the crest and anterior border, is called the anterior superior iliac spine; its outer border gives attachment to the fascia lata, and the Tensor fasciæ latæ, its inner border, to the Iliacus; while its extremity affords attachment to the inguinal ligament and gives origin to the Sartorius. Beneath this eminence is a notch from which the Sartorius takes origin and across which the lateral femoral cutaneous nerve passes. Below the notch is the anterior inferior iliac spine, which ends in the upper lip of the acetabulum; it gives attachment to the straight tendon of the Rectus femoris and to the iliofemoral ligament of the hip-joint. Medial to the anterior inferior spine is a broad, shallow groove, over which the Iliacus and Psoas major pass. This groove is bounded medially by an eminence, the iliopectineal eminence, which marks the point of union of the ilium and pubis. 7
The posterior border of the ala, shorter than the anterior, also presents two projections separated by a notch, the posterior superior iliac spine and the posterior inferior iliac spine. The former serves for the attachment of the oblique portion of the posterior sacroiliac ligaments and the Multifidus; the latter corresponds with the posterior extremity of the auricular surface. Below the posterior inferior spine is a deep notch, the greater sciatic notch. 8

The Ischium (os ischii).—The ischium forms the lower and back part of the hip bone. It is divisible into three portions—a body and two rami. 9

The Body (corpus oss. ischii).—The body enters into and constitutes a little more than two-fifths of the acetabulum. Its external surface forms part of the lunate surface of the acetabulum and a portion of the acetabular fossa. Its internal surface is part of the wall of the lesser pelvis; it gives origin to some fibers of the Obturator internus. Its anterior border projects as the posterior obturator tubercle; from its posterior border there extends backward a thin and pointed triangular eminence, the ischial spine, more or less elongated in different subjects. The external surface of the spine gives attachment to the Gemellus superior, its internal surface to the Coccygeus, Levator ani, and the pelvic fascia; while to the pointed extremity the sacrospinous ligament is attached. Above the spine is a large notch, the greater sciatic notch, converted into a foramen by the sacrospinous ligament; it transmits the Piriformis, the superior and inferior gluteal vessels and nerves, the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels, and nerve, and the nerves to the Obturator internus and Quadratus femoris. Of these, the superior gluteal vessels and nerve pass out above the Piriformis, the other structures below it. Below the spine is a smaller notch, the lesser sciatic notch; it is smooth, coated in the recent state with cartilage, the surface of which presents two or three ridges corresponding to the subdivisions of the tendon of the Obturator internus, which winds over it. It is converted into a foramen by the sacrotuberous and sacrospinous ligaments, and transmits the tendon of the Obturator internus, the nerve which supplies that muscle, and the internal pudendal vessels and nerve. 10

The Superior Ramus (ramus superior oss. ischii; descending ramus).—The superior ramus projects downward and backward from the body and presents for examination three surfaces: external, internal, and posterior. The external surface is quadrilateral in shape. It is bounded above by a groove which lodges the tendon of the Obturator externus; below, it is continuous with the inferior ramus; in front it is limited by the posterior margin of the obturator foramen; behind, a prominent margin separates it from the posterior surface. In front of this margin the surface gives origin to the Quadratus femoris, and anterior to this to some of the fibers of origin of the Obturator externus; the lower part of the surface gives origin to part of the Adductor magnus. The internal surface forms part of the bony wall of the lesser pelvis. In front it is limited by the posterior margin of the obturator foramen. Below, it is bounded by a sharp ridge which gives attachment to a falciform prolongation of the sacrotuberous ligament, and, more anteriorly, gives origin to the Transversus perinæi and Ischiocavernosus. Posteriorly the ramus forms a large swelling, the tuberosity of the ischium, which is divided into two portions: a lower, rough, somewhat triangular part, and an upper, smooth, quadrilateral portion. The lower portion is subdivided by a prominent longitudinal ridge, passing from base to apex, into two parts; the outer gives attachment to the Adductor magnus, the inner to the sacrotuberous ligament. The upper portion is subdivided into two areas by an oblique ridge, which runs downward and outward; from the upper and outer area the Semimembranosus arises; from the lower and inner, the long head of the Biceps femoris and the Semitendinosus. 11

The Inferior Ramus (ramus inferior oss. ischii; ascending ramus).—The inferior ramus is the thin, flattened part of the ischium, which ascends from the superior ramus, and joins the inferior ramus of the pubis—the junction being indicated in the adult by a raised line. The outer surface is uneven for the origin of the Obturator externus and some of the fibers of the Adductor magnus; its inner surface forms part of the anterior wall of the pelvis. Its medial border is thick, rough, slightly everted, forms part of the outlet of the pelvis, and presents two ridges and an intervening space. The ridges are continuous with similar ones on the inferior ramus of the pubis: to the outer is attached the deep layer of the superficial perineal fascia (fascia of Colles), and to the inner the inferior fascia of the urogenital diaphragm. If these two ridges be traced downward, they will be found to join with each other just behind the point of origin of the Transversus perinæi; here the two layers of fascia are continuous behind the posterior border of the muscle. To the intervening space, just in front of the point of junction of the ridges, the Transversus perinæi is attached, and in front of this a portion of the crus penis vel clitoridis and the Ischiocavernosus. Its lateral border is thin and sharp, and forms part of the medial margin of the obturator foramen. 12

The Pubis (os pubis).—The pubis, the anterior part of the hip bone, is divisible into a body, a superior and an inferior ramus. 13

The Body (corpus oss. pubis).—The body forms one-fifth of the acetabulum, contributing by its external surface both to the lunate surface and the acetabular fossa. Its internal surface enters into the formation of the wall of the lesser pelvis and gives origin to a portion of the Obturator internus. 14

The Superior Ramus (ramus superior oss. pubis; ascending ramus).—The superior ramus extends from the body to the median plane where it articulates with its fellow of the opposite side. It is conveniently described in two portions, viz., a medial flattened part and a narrow lateral prismoid portion. 15
The Medial Portion of the superior ramus, formerly described as the body of the pubis, is somewhat quadrilateral in shape, and presents for examination two surfaces and three borders. The anterior surface is rough, directed downward and outward, and serves for the origin of various muscles. The Adductor longus arises from the upper and medial angle, immediately below the crest; lower down, the Obturator externus, the Adductor brevis, and the upper part of the Gracilis take origin. The posterior surface, convex from above downward, concave from side to side, is smooth, and forms part of the anterior wall of the pelvis. It gives origin to the Levator ani and Obturator internus, and attachment to the puboprostatic ligaments and to a few muscular fibers prolonged from the bladder. The upper border presents a prominent tubercle, the pubic tubercle (pubic spine), which projects forward; the inferior crus of the subcutaneous inguinal ring (external abdominal ring), and the inguinal ligament (Poupart’s ligament) are attached to it. Passing upward and lateralward from the pubic tubercle is a well-defined ridge, forming a part of the pectineal line which marks the brim of the lesser pelvis: to it are attached a portion of the inguinal falx (conjoined tendon of Obliquus internus and Transversus), the lacunar ligament (Gimbernat’s ligament), and the reflected inguinal ligament (triangular fascia). Medial to the pubic tubercle is the crest, which extends from this process to the medial end of the bone. It affords attachment to the inguinal falx, and to the Rectus abdominis and Pyramidalis. The point of junction of the crest with the medial border of the bone is called the angle; to it, as well as to the symphysis, the superior crus of the subcutaneous inguinal ring is attached. The medial border is articular; it is oval, and is marked by eight or nine transverse ridges, or a series of nipple-like processes arranged in rows, separated by grooves; they serve for the attachment of a thin layer of cartilage, which intervenes between it and the interpubic fibrocartilaginous lamina. The lateral border presents a sharp margin, the obturator crest, which forms part of the circumference of the obturator foramen and affords attachment to the obturator membrane. 16
The Lateral Portion of the ascending ramus has three surfaces: superior, inferior, andposterior. The superior surface presents a continuation of the pectineal line, already mentioned as commencing at the pubic tubercle. In front of this line, the surface of bone is triangular in form, wider laterally than medially, and is covered by the Pectineus. The surface is bounded, laterally, by a rough eminence, the iliopectineal eminence, which serves to indicate the point of junction of the ilium and pubis, and below by a prominent ridge which extends from the acetabular notch to the pubic tubercle. The inferior surface forms the upper boundary of the obturator foramen, and presents, laterally, a broad and deep, oblique groove, for the passage of the obturator vessels and nerve; and medially, a sharp margin, the obturator crest, forming part of the circumference of the obturator foramen, and giving attachment to the obturator membrane. The posterior surface constitutes part of the anterior boundary of the lesser pelvis. It is smooth, convex from above downward, and affords origin to some fibers of the Obturator internus. 17

The Inferior Ramus (ramus inferior oss. pubis; descending ramus).—The inferior ramus is thin and flattened. It passes lateralward and downward from the medial end of the superior ramus; it becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen. Its anterior surface is rough, for the origin of muscles—the Gracilis along its medial border, a portion of the Obturator externus where it enters into the formation of the obturator foramen, and between these two, the Adductores brevis and magnus, the former being the more medial. The posterior surface is smooth, and gives origin to the Obturator internus, and, close to the medial margin, to the Constrictor urethræ. The medial border is thick, rough, and everted, especially in females. It presents two ridges, separated by an intervening space. The ridges extend downward, and are continuous with similar ridges on the inferior ramus of the ischium; to the external is attached the fascia of Colles, and to the internal the inferior fascia of the urogenital diaphragm. The lateral border is thin and sharp, forms part of the circumference of the obturator foramen, and gives attachment to the obturator membrane. 18

The Acetabulum (cotyloid cavity).—The acetabulum is a deep, cup-shaped, hemispherical depression, directed downward, lateralward, and forward. It is formed medially by the pubis, above by the ilium, laterally and below by the ischium; a little less than two-fifths is contributed by the ilium, a little more than two-fifths by the ischium, and the remaining fifth by the pubis. It is bounded by a prominent uneven rim, which is thick and strong above, and serves for the attachment of the glenoidal labrum (cotyloid ligament), which contracts its orifice, and deepens the surface for articulation. It presents below a deep notch, the acetabular notch, which is continuous with a circular non-articular depression, the acetabular fossa, at the bottom of the cavity: this depression is perforated by numerous apertures, and lodges a mass of fat. The notch is converted into a foramen by the transverse ligament; through the foramen nutrient vessels and nerves enter the joint; the margins of the notch serve for the attachment of the ligamentum teres. The rest of the acetabulum is formed by a curved articular surface, the lunate surface, for articulation with the head of the femur. 19

The Obturator Foramen (foramen obturatum; thyroid foramen).—The obturator foramen is a large aperture, situated between the ischium and pubis. In the male it is large and of an oval form, its longest diameter slanting obliquely from before backward; in the female it is smaller, and more triangular. It is bounded by a thin, uneven margin, to which a strong membrane is attached, and presents, superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely medialward and downward. This groove is converted into a canal by a ligamentous band, a specialized part of the obturator membrane, attached to two tubercles: one, the posterior obturator tubercle, on the medial border of the ischium, just in front of the acetabular notch; the other, the anterior obturator tubercle, on the obturator crest of the superior ramus of the pubis. Through the canal the obturator vessels and nerve pass out of the pelvis. 20

Structure.—The thicker parts of the bone consist of cancellous tissue, enclosed between two layers of compact tissue; the thinner parts, as at the bottom of the acetabulum and center of the iliac fossa, are usually semitransparent, and composed entirely of compact tissue. 21

Ossification (Fig. 237).—The hip bone is ossified from eight centers: three primary—one each for the ilium, ischium, and pubis; and five secondary—one each for the crest of the ilium, the anterior inferior spine (said to occur more frequently in the male than in the female), the tuberosity of the ischium, the pubic symphysis (more frequent in the female than in the male), and one or more for the Y-shaped piece at the bottom of the acetabulum. The centers appear in the following order: in the lower part of the ilium, immediately above the greater sciatic notch, about the eighth or ninth week of fetal life; in the superior ramus of the ischium, about the third month; in the superior ramus of the pubis, between the fourth and fifth months. At birth, the three primary centers are quite separate, the crest, the bottom of the acetabulum, the ischial tuberosity, and the inferior rami of the ischium and pubis being still cartilaginous. By the seventh or eighth year, the inferior rami of the pubis and ischium are almost completely united by bone. About the thirteenth or fourteenth year, the three primary centers have extended their growth into the bottom of the acetabulum, and are there separated from each other by a Y-shaped portion of cartilage, which now presents traces of ossification, often by two or more centers. One of these, the os acetabuli, appears about the age of twelve, between the ilium and pubis, and fuses with them about the age of eighteen; it forms the pubic part of the acetabulum. The ilium and ischium then become joined, and lastly the pubis and ischium, through the intervention of this Y-shaped portion. At about the age of puberty, ossification takes place in each of the remaining portions, and they join with the rest of the bone between the twentieth and twenty-fifth years. Separate centers are frequently found for the pubic tubercle and the ischial spine, and for the crest and angle of the pubis. 22

Articulations.—The hip bone articulates with its fellow of the opposite side, and with the sacrum and femur. 23

FIG. 237– Plan of ossification of the hip bone. The three primary centers unite through a Y-shaped piece about puberty. Epiphyses appear about puberty, and unite about twenty-fifth year. (See enlarged image)

6c. 2. The Pelvis

The pelvis, so called from its resemblance to a basin, is a bony ring, interposed between the movable vertebræ of the vertebral column which it supports, and the lower limbs upon which it rests; it is stronger and more massively constructed than the wall of the cranial or thoracic cavities, and is composed of four bones: the two hip bones laterally and in front and the sacrum and coccyx behind.
The pelvis is divided by an oblique plane passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the symphysis pubis, into the greater and the lesser pelvis. The circumference of this plane is termed the linea terminalis or pelvic brim.

The Greater or False Pelvis (pelvis major).—The greater pelvis is the expanded portion of the cavity situated above and in front of the pelvic brim. It is bounded on either side by the ilium; in front it is incomplete, presenting a wide interval between the anterior borders of the ilia, which is filled up in the fresh state by the parietes of the abdomen; behind is a deep notch on either side between the ilium and the base of the sacrum. It supports the intestines, and transmits part of their weight to the anterior wall of the abdomen.

The Lesser or True Pelvis (pelvis minor).—The lesser pelvis is that part of the pelvic cavity which is situated below and behind the pelvic brim. Its bony walls are more complete than those of the greater pelvis. For convenience of description, it is divided into an inlet bounded by the superior circumference, and outlet bounded by the inferior circumference, and a cavity.

The Superior Circumference.—The superior circumference forms the brim of the pelvis, the included space being called the superior aperture or inlet (apertura pelvis [minoris] superior) (Fig. 238). It is formed laterally by the pectineal and arcuate lines, in front by the crests of the pubes, and behind by the anterior margin of the base of the sacrum and sacrovertebral angle. The superior aperture is somewhat heart-shaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum. It has three principal diameters: antero-posterior, transverse, and oblique. The anteroposterior or conjugate diameter extends from the sacrovertebral angle to the symphysis pubis; its average measurement is about 110 mm. in the female. The transverse diameter extends across the greatest width of the superior aperture, from the middle of the brim on one side to the same point on the opposite; its average measurement is about 135 mm. in the female. The oblique diameter extends from the iliopectineal eminence of one side to the sacroiliac articulation of the opposite side; its average measurement is about 125 mm. in the female. 5

FIG. 238– Diameters of superior aperture of lesser pelvis (female). (See enlarged image)

The cavity of the lesser pelvis is bounded in front and below by the pubic symphysis and the superior rami of the pubes; above and behind, by the pelvic surfaces of the sacrum and coccyx, which, curving forward above and below, contract the superior and inferior apertures of the cavity; laterally, by a broad, smooth, quadrangular area of bone, corresponding to the inner surfaces of the body and superior ramus of the ischium and that part of the ilium which is below the arcuate line. From this description it will be seen that the cavity of the lesser pelvis is a short, curved canal, considerably deeper on its posterior than on its anterior wall. It contains, in the fresh subject, the pelvic colon, rectum, bladder, and some of the organs of generation. The rectum is placed at the back of the pelvis, in the curve of the sacrum and coccyx; the bladder is in front, behind the pubic symphysis. In the female the uterus and vagina occupy the interval between these viscera. 6

The Lower Circumference.—The lower circumference of the pelvis is very irregular; the space enclosed by it is named the inferior aperture or outlet (apertura pelvis [minoris] inferior) (Fig. 239), and is bounded behind by the point of the coccyx, and laterally by the ischial tuberosities. These eminences are separated by three notches: one in front, the pubic arch, formed by the convergence of the inferior rami of the ischium and pubis on either side. The other notches, one on either side, are formed by the sacrum and coccyx behind, the ischium in front, and the ilium above; they are called the sciatic notches; in the natural state they are converted into foramina by the sacrotuberous and sacrospinous ligaments. When the ligaments are in situ, the inferior aperture of the pelvis is lozenge-shaped, bounded, in front, by the pubic arcuate ligament and the inferior rami of the pubes and ischia; laterally, by the ischial tuberosities; and behind, by the sacrotuberous ligaments and the tip of the coccyx. 7

FIG. 239– Diameters of inferior aperture of lesser pelvis (female). (See enlarged image)

The diameters of the outlet of the pelvis are two, antero-posterior and transverse. The antero-posterior diameter extends from the tip of the coccyx to the lower part of the pubic symphysis; its measurement is from 90 to 115 mm. in the female. It varies with the length of the coccyx, and is capable of increase or diminution, on account of the mobility of that bone. The transverse diameter, measured between the posterior parts of the ischial tuberosities, is about 115 mm. in the female. 58 8

FIG. 240– Median sagittal section of pelvis. (See enlarged image)

Axes (Fig. 240).—A line at right angles to the plane of the superior aperture at its center would, if prolonged, pass through the umbilicus above and the middle of the coccyx below; the axis of the superior aperture is therefore directed downward and backward. The axis of the inferior aperture, produced upward, would touch the base of the sacrum, and is also directed downward, and slightly backward. The axis of the cavity—i. e., an axis at right angles to a series of planes between those of the superior and inferior apertures —is curved like the cavity itself: this curve corresponds to the concavity of the sacrum and coccyx, the extremities being indicated by the central points of the superior and inferior apertures. A knowledge of the direction of these axes serves to explain the course of the fetus in its passage through the pelvis during parturition. 9

Position of the Pelvis (Fig. 240).—In the erect posture, the pelvis is placed obliquely with regard to the trunk: the plane of the superior aperture forms an angle of from 50° to 60°, and that of the inferior aperture one of about 15° with the horizontal plane. The pelvic surface of the symphysis pubis looks upward and backward, the concavity of the sacrum and coccyx downward and forward. The position of the pelvis in the erect posture may be indicated by holding it so that the anterior superior iliac spines and the front of the top of the symphysis pubis are in the same vertical plane. 10

FIG. 241– Male pelvis. (See enlarged image)

Differences between the Male and Female Pelves.—The female pelvis (Fig. 242) is distinguished from that of the male (Fig. 241) by its bones being more delicate and its depth less. The whole pelvis is less massive, and its muscular impressions are slightly marked. The ilia are less sloped, and the anterior iliac spines more widely separated; hence the greater lateral prominence of the hips. The preauricular sulcus is more commonly present and better marked. The superior aperture of the lesser pelvis is larger in the female than in the male; it is more nearly circular, and its obliquity is greater. The cavity is shallower and wider; the sacrum is shorter wider, and its upper part is less curved; the obturator foramina are triangular in shape and smaller in size than in the male. The inferior aperture is larger and the coccyx more movable. The sciatic notches are wider and shallower, and the spines of the ischia project less inward. The acetabula are smaller and look more distinctly forward (Derry 59). The ischial tuberosities and the acetabula are wider apart, and the former are more everted. The pubic symphysis is less deep, and the pubic arch is wider and more rounded than in the male, where it is an angle rather than an arch. 11
The size of the pelvis varies not only in the two sexes, but also in different members of the same sex, and does not appear to be influenced in any way by the height of the individual. Women of short stature, as a rule, have broad pelves. Occasionally the pelvis is equally contracted in all its dimensions, so much so that all its diameters measure 12.5 mm. less than the average, and this even in well-formed women of average height. The principal divergences, however, are found at the superior aperture, and affect the relation of the antero-posterior to the transverse diameter. Thus the superior aperture may be elliptical either in a transverse or an antero-posterior direction, the transverse diameter in the former, and the antero-posterior in the latter, greatly exceeding the other diameters; in other instances it is almost circular. 12

FIG. 242– Female pelvis. (See enlarged image)

In the fetus, and for several years after birth, the pelvis is smaller in proportion than in the adult, and the projection of the sacrovertebral angle less marked. The characteristic differences between the male and female pelvis are distinctly indicated as early as the fourth month of fetal life. 13

Abnormalities.—There is arrest of development in the bones of the pelvis in cases of extroversion of the bladder; the anterior part of the pelvic girdle is deficient, the superior rami of the pubes are imperfectly developed, and the symphysis is absent. “The pubic bones are separated to the extent of from two to four inches, the superior rami shortened and directed forward, and the obturator foramen diminished in size, narrowed, and turned outward. The iliac bones are straightened out more than normal. The sacrum is very peculiar. The lateral curve, instead of being concave, is flattened out or even convex, with the iliosacral facets turned more outward than normal, while the vertical curve is straightened.” 60 14
Note 58. The measurements of the pelvis given above are fairly accurate, but different figures are given by various authors no doubt due mainly to differences in the physique and stature of the population from whom the measurements have been taken. [back]
Note 59. Journal of Anatomy and Physiology, vol. xliii. [back]
Note 60. Wood, Heath’s Dictionary of Practical Surgery, i, 426. [back]

6c. 3. The Femur

(Thigh Bone)

The femur (Figs. 244, 245), the longest and strongest bone in the skeleton, is almost perfectly cylindrical in the greater part of its extent. In the erect posture it is not vertical, being separated above from its fellow by a considerable interval, which corresponds to the breadth of the pelvis, but inclining gradually downward and medialward, so as to approach its fellow toward its lower part, for the purpose of bringing the knee-joint near the line of gravity of the body. The degree of this inclination varies in different persons, and is greater in the female than in the male, on account of the greater breadth of the pelvis. The femur, like other long bones, is divisible into a body and two extremities.

The Upper Extremity (proximal extremity, Fig. 243).—The upper extremity presents for examination a head, a neck, a greater and a lesser trochanter.

The Head (caput femoris).—The head which is globular and forms rather more than a hemisphere, is directed upward, medialward, and a little forward, the greater part of its convexity being above and in front. Its surface is smooth, coated with cartilage in the fresh state, except over an ovoid depression, the fovea capitis femoris, which is situated a little below and behind the center of the head, and gives attachment to the ligamentum teres.

The Neck (collum femoris).—The neck is a flattened pyramidal process of bone, connecting the head with the body, and forming with the latter a wide angle opening medialward. The angle is widest in infancy, and becomes lessened during growth, so that at puberty it forms a gentle curve from the axis of the body of the bone. In the adult, the neck forms an angle of about 125° with the body, but this varies in inverse proportion to the development of the pelvis and the stature. In the female, in consequence of the increased width of the pelvis, the neck of the femur forms more nearly a right angle with the body than it does in the male. The angle decreases during the period of growth, but after full growth has been attained it does not usually undergo any change, even in old age; it varies considerably in different persons of the same age. It is smaller in short than in long bones, and when the pelvis is wide. In addition to projecting upward and medialward from the body of the femur, the neck also projects somewhat forward; the amount of this forward projection is extremely variable, but on an average is from 12° to 14°. 4

FIG. 243– Upper extremity of right femur viewed from behind and above. (See enlarged image)

The neck is flattened from before backward, contracted in the middle, and broader laterally than medially. The vertical diameter of the lateral half is increased by the obliquity of the lower edge, which slopes downward to join the body at the level of the lesser trochanter, so that it measures one-third more than the antero-posterior diameter. The medial half is smaller and of a more circular shape. The anterior surface of the neck is perforated by numerous vascular foramina. Along the upper part of the line of junction of the anterior surface with the head is a shallow groove, best marked in elderly subjects; this groove lodges the orbicular fibers of the capsule of the hip-joint. The posterior surface is smooth, and is broader and more concave than the anterior: the posterior part of the capsule of the hip-joint is attached to it about 1 cm. above the intertrochanteric crest. The superior border is short and thick, and ends laterally at the greater trochanter; its surface is perforated by large foramina. The inferior border, long and narrow, curves a little backward, to end at the lesser trochanter. 5

The Trochanters.—The trochanters are prominent processes which afford leverage to the muscles that rotate the thigh on its axis. They are two in number, the greater and the lesser. 6

FIG. 244– Right femur. Anterior surface. (See enlarged image)

The Greater Trochanter (trochanter major; great trochanter) is a large, irregular, quadrilateral eminence, situated at the junction of the neck with the upper part of the body. It is directed a little lateralward and backward, and, in the adult, is about 1 cm. lower than the head. It has two surfaces and four borders. The lateral surface, quadrilateral in form, is broad, rough, convex, and marked by a diagonal impression, which extends from the postero-superior to the antero-inferior angle, and serves for the insertion of the tendon of the Glutæus medius. Above the impression is a triangular surface, sometimes rough for part of the tendon of the same muscle, sometimes smooth for the interposition of a bursa between the tendon and the bone. Below and behind the diagonal impression is a smooth, triangular surface, over which the tendon of the Glutæus maximus plays, a bursa being interposed. The medial surface, of much less extent than the lateral, presents at its base a deep depression, the trochanteric fossa (digital fossa), for the insertion of the tendon of the Obturator externus, and above and in front of this an impression for the insertion of the Obsturator internus and Gemelli. The superior border is free; it is thick and irregular, and marked near the center by an impression for the insertion of the Piriformis. The inferior border corresponds to the line of junction of the base of the trochanter with the lateral surface of the body; it is marked by a rough, prominent, slightly curved ridge, which gives origin to the upper part of the Vastus lateralis. The anterior border is prominent and somewhat irregular; it affords insertion at its lateral part to the Glutæus minimus. The posterior border is very prominent and appears as a free, rounded edge, which bounds the back part of the trochanteric fossa. 7
The Lesser Trochanter (trochanter minor; small trochanter) is a conical eminence, which varies in size in different subjects; it projects from the lower and back part of the base of the neck. From its apex three well-marked borders extend; two of these are above—a medial continuous with the lower border of the neck, a lateral with the intertrochanteric crest; the inferior border is continuous with the middle division of the linea aspera. The summit of the trochanter is rough, and gives insertion to the tendon of the Psoas major. 8
A prominence, of variable size, occurs at the junction of the upper part of the neck with the greater trochanter, and is called the tubercle of the femur; it is the point of meeting of five muscles: the Glutæus minimus laterally, the Vastus lateralis below, and the tendon of the Obturator internus and two Gemelli above. Running obliquely downward and medialward from the tubercle is the intertrochanteric line (spiral line of the femur); it winds around the medial side of the body of the bone, below the lesser trochanter, and ends about 5 cm. below this eminence in the linea aspera. Its upper half is rough, and affords attachment to the iliofemoral ligament of the hip-joint; its lower half is less prominent, and gives origin to the upper part of the Vastus medialis. Running obliquely downward and medialward from the summit of the greater trochanter on the posterior surface of the neck is a prominent ridge, the intertrochanteric crest. Its upper half forms the posterior border of the greater trochanter, and its lower half runs downward and medialward to the lesser trochanter. A slight ridge is sometimes seen commencing about the middle of the intertrochanteric’ crest, and reaching vertically downward for about 5 cm. along the back part of the body: it is called the linea quadrata, and gives attachment to the Quadratus femoris and a few fibers of the Adductor magnus. Generally there is merely a slight thickening about the middle of the intertrochanteric crest, marking the attachment of the upper part of the Quadratus femoris. 9

FIG. 245– Right femur. Posterior surface. (See enlarged image)

The Body or Shaft (corpus femoris).—The body, almost cylindrical in form, is a little broader above than in the center, broadest and somewhat flattened from before backward below. It is slightly arched, so as to be convex in front, and concave behind, where it is strengthened by a prominent longitudinal ridge, the linea aspera. It presents for examination three borders, separating three surfaces. Of the borders, one, the linea aspera, is posterior, one is medial, and the other, lateral. 10
The linea aspera (Fig. 245) is a prominent longitudinal ridge or crest, on the middle third of the bone, presenting a medial and a lateral lip, and a narrow rough, intermediate line. Above, the linea aspera is prolonged by three ridges. The lateral ridge is very rough, and runs almost vertically upward to the base of the greater trochanter. It is termed the gluteal tuberosity, and gives attachment to part of the Glutæus maximus: its upper part is often elongated into a roughened crest, on which a more or less well-marked, rounded tubercle, the third trochanter, is occasionally developed. The intermediate ridge or pectineal line is continued to the base of the lesser trochanter and gives attachment to the Pectineus; the medial ridge is lost in the intertrochanteric line; between these two a portion of the Iliacus is inserted. Below, the linea aspera is prolonged into two ridges, enclosing between them a triangular area, the popliteal surface, upon which the popliteal artery rests. Of these two ridges, the lateral is the more prominent, and descends to the summit of the lateral condyle. The medial is less marked, especially at its upper part, where it is crossed by the femoral artery. It ends below at the summit of the medial condyle, in a small tubercle, the adductor tubercle, which affords insertion to the tendon of the Adductor magnus. 11
From the medial lip of the linea aspera and its prolongations above and below, the Vastus medialis arises; and from the lateral lip and its upward prolongation, the Vastus lateralis takes origin. The Adductor magnus is inserted into the linea aspera, and to its lateral prolongation above, and its medial prolongation below. Between the Vastus lateralis and the Adductor magnus two muscles are attached—viz., the Glutæus maximus inserted above, and the short head of the Biceps femoris arising below. Between the Adductor magnus and the Vastus medialis four muscles are inserted: the Iliacus and Pectineus above; the Adductor brevis and Adductor longus below. The linea aspera is perforated a little below its center by the nutrient canal, which is directed obliquely upward. 12
The other two borders of the femur are only slightly marked: the lateral border extends from the antero-inferior angle of the greater trochanter to the anterior extremity of the lateral condyle; the medial border from the intertrochanteric line, at a point opposite the lesser trochanter, to the anterior extremity of the medial condyle. 13
The anterior surface includes that portion of the shaft which is situated between the lateral and medial borders. It is smooth, convex, broader above and below than in the center. From the upper three-fourths of this surface the Vastus intermedius arises; the lower fourth is separated from the muscle by the intervention of the synovial membrane of the knee-joint and a bursa; from the upper part of it the Articularis genu takes origin. The lateral surface includes the portion between the lateral border and the linea aspera; it is continuous above with the corresponding surface of the greater trochanter, below with that of the lateral condyle: from its upper three-fourths the Vastus intermedius takes origin. The medial surface includes the portion between the medial border and the linea aspera; it is continuous above with the lower border of the neck, below with the medial side of the medial condyle: it is covered by the Vastus medialis. 14

FIG. 246– Lower extremity of right femur viewed from below. (See enlarged image)

The Lower Extremity (distal extremity), (Fig. 246).—The lower extremity, larger than the upper, is somewhat cuboid in form, but its transverse diameter is greater than its antero-posterior; it consists of two oblong eminences known as the condyles. In front, the condyles are but slightly prominent, and are separated from one another by a smooth shallow articular depression called the patellar surface; behind, they project considerably, and the interval between them forms a deep notch, the intercondyloid fossa. The lateral condyle is the more prominent and is the broader both in its antero-posterior and transverse diameters, the medial condyle is the longer and, when the femur is held with its body perpendicular, projects to a lower level. When, however, the femur is in its natural oblique position the lower surfaces of the two condyles lie practically in the same horizontal plane. The condyles are not quite parallel with one another; the long axis of the lateral is almost directly antero-posterior, but that of the medial runs backward and medialward. Their opposed surfaces are small, rough, and concave, and form the walls of the intercondyloid fossa. This fossa is limited above by a ridge, the intercondyloid line, and below by the central part of the posterior margin of the patellar surface. The posterior cruciate ligament of the knee-joint is attached to the lower and front part of the medial wall of the fossa and the anterior cruciate ligament to an impression on the upper and back part of its lateral wall. Each condyle is surmounted by an elevation, the epicondyle. The medial epicondyle is a large convex eminence to which the tibial collateral ligament of the knee-joint is attached. At its upper part is the adductor tubercle, already referred to, and behind it is a rough impression which gives origin to the medial head of the Gastrocnemius. The lateral epicondyle, smaller and less prominent than the medial, gives attachment to the fibular collateral ligament of the knee-joint. Directly below it is a small depression from which a smooth well-marked groove curves obliquely upward and backward to the posterior extremity of the condyle. This groove is separated from the articular surface of the condyle by a prominent lip across which a second, shallower groove runs vertically downward from the depression. In the fresh state these grooves are covered with cartilage. The Popliteus arises from the depression; its tendon lies in the oblique groove when the knee is flexed and in the vertical groove when the knee is extended. Above and behind the lateral epicondyle is an area for the origin of the lateral head of the Gastrocnemius, above and to the medial side of which the Plantaris arises. 15
The articular surface of the lower end of the femur occupies the anterior, inferior, and posterior surfaces of the condyles. Its front part is named the patellar surface and articulates with the patella; it presents a median groove which extends downward to the intercondyloid fossa and two convexities, the lateral of which is broader, more prominent, and extends farther upward than the medial. The lower and posterior parts of the articular surface constitute the tibial surfaces for articulation with the corresponding condyles of the tibia and menisci. These surfaces are separated from one another by the intercondyloid fossa and from the patellar surface by faint grooves which extend obliquely across the condyles. The lateral groove is the better marked; it runs lateralward and forward from the front part of the intercondyloid fossa, and expands to form a triangular depression. When the knee-joint is fully extended, the triangular depression rests upon the anterior portion of the lateral meniscus, and the medial part of the groove comes into contact with the medial margin of the lateral articular surface of the tibia in front of the lateral tubercle of the tibial intercondyloid eminence. The medial groove is less distinct than the lateral. It does not reach as far as the intercondyloid fossa and therefore exists only on the medial part of the condyle; it receives the anterior edge of the medial meniscus when the knee-joint is extended. Where the groove ceases laterally the patellar surface is seen to be continued backward as a semilunar area close to the anterior part of the intercondyloid fossa; this semilunar area articulates with the medial vertical facet of the patella in forced flexion of the knee-joint. The tibial surfaces of the condyles are convex from side to side and from before backward. Each presents a double curve, its posterior segment being an arc of a circle, its anterior, part of a cycloid. 61 16

The Architecture of the Femur.—Koch 62 by mathematical analysis has “shown that in every part of the femur there is a remarkable adaptation of the inner structure of the bone to the machanical requirements due to the load on the femur-head. The various parts of the femur taken together form a single mechanical structure wonderfully well-adapted for the efficient, economical transmission of the loads from the acetabulum to the tibia; a structure in which every element contributes its modicum of strength in the manner required by theoretical mechanics for maximum efficiency.” “The internal structure is everywhere so formed as to provide in an efficient manner for all the internal stresses which occur due to the load on the femur-head. Throughout the femur, with the load on the femur-head, the bony material is arranged in the paths of the maximum internal stresses, which are thereby resisted with the greatest efficiency, and hence with maximum economy of material.” “The conclusion is inevitable that the inner structure and outer form of the femur are governed by the conditions of maximum stress to which the bone is subjected normally by the preponderant load on the femur-head; that is, by the body weight transmitted to the femur-head through the acetabulum.” “The femur obeys the mechanical laws that govern other elastic bodies under stress; the relation between the computed internal stresses due to the load on the femur-head, and the internal structure of the different portions of the femur is in very close agreement with the theoretical relations that should exist between stress and structure for maximum economy and efficiency; and, therefore, it is believed that the following laws of bone structure have been demonstrated for the femur: 17
“1. The inner structure and external form of human bone are closely adapted to the mechanical conditions existing at every point in the bone. 18
“2. The inner architecture of normal bone is determined by definite and exact requirements of mathematical and mechanical laws to produce a maximum of strength with a minimum of material.” 19

The Inner Architecture of the Upper Femur.—“The spongy bone of the upper femur (to the lower limit of the lesser trochanter) is composed of two distinct systems of trabeculæ arranged in curved paths: one, which has its origin in the medial (inner) side of the shaft and curving upward in a fan-like radiation to the opposite side of the bone; the other, having origin in the lateral (outer) portion of the shaft and arching upward and medially to end in the upper surface of the greater trochanter, neck and head. These two systems intersect each other at right angles. 20
“A. Medial (Compressive) System of Trabeculæ.—As the compact bone of the medial (inner) part of the shaft nears the head of the femur it gradually becomes thinner and finally reaches the articular surface of the head as a very thin layer. From a point at about the lower level of the lesser trochanter, 2 1/2 to 3 inches from the lower limit of the articular surface of the head, the trabeculæ branch off from the shaft in smooth curves, spreading radially to cross to the opposite side in two well-defined groups: a lower, or secondary group, and an upper, or principal group. 21

FIG. 247– Frontal longitudinal midsection of upper femur. (See enlarged image)

“a. The Secondary Compressive Group.—This group of trabeculæ leaves the inner border of the shaft beginning at about the level of the lesser trochanter, and for a distance of almost 2 inches along the curving shaft, with which the separate trabeculæ make an angle of about 45 degrees. They curve outwardly and upwardly to cross in radiating smooth curves to the opposite side. The lower filaments end in the region of the greater trochanter: the adjacent filaments above these pursue a more nearly vertical course and end in the upper portion of the neck of the femur. The trabeculæ of this group are thin and with wide spaces between them. As they traverse the space between the medial and lateral surfaces of the bone they cross at right angles the system of curved trabeculæ which arise from the lateral (outer) portion of the shaft. (Figs. 247 and 249.) 22
“b. The Principal Compressive Group.—This group of trabeculæ (Figs. 247 and 249.) springs from the medial portion of the shaft just above the group above-described, and spreads upward and in slightly radial smooth curved lines to reach the upper portion of the articular surface of the head of the femur. These trabeculæ are placed very closely together and are the thickest ones seen in the upper femur. They are a prolongation of the shaft from which they spring in straight lines which gradually curve to meet at right-angles the articular surface. There is no change as they cross the epiphyseal line. They also intersect at right-angles the system of lines which rise from the lateral side of the femur. 23

FIG. 248– Diagram of the lines of stress in the upper femur, based upon the mathematical analysis of the right femur. These result from the combination of the different kinds of stresses at each point in the femur. (After Koch.) (See enlarged image)

“This system of principal and secondary compressive trabeculæ corresponds in position and in curvature with the lines of maximum compressive stress, which were traced out in the mathematical analysis of this portion of the femur. (Figs. 247 and 250.) 24
“B. Lateral (Tensile) System of Trabeculæ.—As the compact bone of the outer portion of the shaft approaches the greater trochanter it gradually decreases in thickness. Beginning at a point about 1 inch below the level of the lower border of the greater trochanter, numerous thin trabeculæ are given off from the outer portion of the shaft. These trabeculæ lie in three distinct groups. 25
“c. The Greater Trochanter Group.—These trabeculæ rise from the outer part of the shaft just below the greater trochanter and rise in thin, curving lines to cross the region of the greater trochanter and end in its upper surface. Some of these filaments are poorly defined. This group intersects the trabeculæ of group (a) which rise from the opposite side. The trabeculæ of this group evidently carry small stresses, as is shown by their slenderness. 26

FIG. 249– Frontal longitudinal midsection of left femur. Taken from the same subject as the one that was analyzed and shown in Figs. 248 and 250. 4/9 of natural size. (After Koch.) (See enlarged image)

FIG. 250– Diagram of the computed lines of maximum stress in the normal femur. The section numbers 2, 4, 6, 8, etc., show the positions of the transverse sections analyzed. The amounts of the maximum tensile and compressive stress at the various sections are given for a load of 100 pounds on the femur-head. For the standing position (“at attention”) these stresses are multiplied by 0.6, for walking by 1.6 and for running by 3.2. (After Koch.) (See enlarged image)

“d. The Principal Tensile Group.—This group springs from the outer part of the shaft immediately below group c, and curves convexly upward and inward in nearly parallel lines across the neck of the femur and ends in the inferior portion of the head. These trabeculæ are somewhat thinner and more, widely spaced than those of the principal compressive group (b). All the trabeculæ of this group cross those of groups (a) and (b) at right angles. This group is the most important of the lateral system (tensile) and, as will be shown later, the greatest tensile stresses of the upper femur are carried by the trabeculæ of this group. 27
“e. The Secondary Tensile Group.—This group consists of the trabeculæ which spring from the outer side of the shaft and lie below those of the preceding group. They curve upward and medially across the axis of the femur and end more or less irregularly after crossing the midline, but a number of these filaments end in the medial portion of the shaft and neck. They cross at right angles the trabeculæ of group (a). 28

FIG. 251– Intensity of the maximum tensile and compressive stresses in the upper femur. Computed for the load of 100 pounds on the right femur. Corresponds to the upper part of Fig. 250. (After Koch.) (See enlarged image)

“In general, the trabeculæ of the tensile system are lighter in structure than those of the compressive system in corresponding positions. The significance of the difference in thickness of these two systems is that the thickness of the trabeculæ varies with the intensity of the stresses at any given point. Comparison of Fig. 247 with Fig. 251 will show that the trabeculæ of the compressive system carry heavier stresses than those of the tensile system in corresponding positions. For example, the maximum tensile stress at section 8 (Fig. 251) in the outermost fiber is 771 pounds per square inch, and at the corresponding point on the compressive side the compressive stress is 954 pounds per square inch. Similar comparisons may be made at other points, which confirm the conclusion that the thickness and closeness of spacing of the trabeculæ varies in proportion to the intensity of the stresses carried by them. 29
“It will be seen that the trabeculæ lie exactly in the paths of the maximum tensile and compressive stresses (compare Figs. 247, 248 and 251), and hence these trabeculæ carry these stresses in the most economical manner. This is in accordance with the well-recognized principle of mechanics that the most direct manner of transmitting stress is in the direction in which the stress acts. 30
“Fig. 249 shows a longitudinal frontal section through the left femur, which is the mate of the right femur on which the mathematical analysis was made. In this midsection the system of tensile trabeculæ, which rises from the lateral (outer) part of the shaft and crosses over the central area to end in the medial portion of the shaft, neck and head, is clearly shown. This figure also shows the compressive system of trabeculæ which rises on the medial portion of the shaft and crosses the central area to end in the head, neck and greater trochanter. By comparing the position of these two systems of trabeculæ shown in Fig. 249 with the lines of maximum and minimum stresses shown in Figs. 248 and 250 it is seen that the tensile system of trabeculæ corresponds exactly with the position of the lines of maximum and minimum tensile stresses which were determined by mathematical analysis. In a similar manner, the compressive system of trabeculæ in Fig. 249 corresponds exactly with the lines of maximum and minimum compressive stresses computed by mathematical analysis. 31
“The amount of vertical shear varies almost uniformly from a maximum of 90 pounds (90 percent. of the load on the femur-head) midway between sections 4 and 6, to a minimum of —5.7 pounds at section 18” (Fig. 251). There is a gradual diminution of the spongy bone from section 6 to section 18 parallel with the diminished intensities of the vertical shear. 32
1. The trabeculæ of the upper femur, as shown in frontal sections, are arranged in two general systems, compressive and tensile, which correspond in position with the lines of maximum and minimum stresses in the femur determined by the mathematical analysis of the femur as a mechanical structure. 33
2. The thickness and spacing of the trabeculæ vary with the intensity of the maximum stresses at various points in the upper femur, being thickest and most closely spaced in the regions where the greatest stresses occur. 34
3. The amount of bony material in the spongy bone of the upper femur varies in proportion to the intensity of the shearing force at the various sections. 35
4. The arrangement of the trabeculæ in the positions of maximum stresses is such that the greatest strength is secured with a minimum of material. 36
Significance of the Inner Architecture of the Shaft.—1. Economy for resisting shear. The shearing stresses are at a minimum in the shaft. “It is clear that a minimum amount of material will be required to resist the shearing stresses.” As horizontal and vertical shearing stresses are most efficiently resisted by material placed near the neutral plane, in this region a minimum amount of material will be needed near the neutral axis. In the shaft there is very little if any material in the central space, practically the only material near the neutral plane being in the compact bone, but lying at a distance from the neutral axis. This conforms to the requirement of mechanics for economy, as a minimum of material is provided for resisting shearing stresses where these stresses are a minimum. 37
2. Economy for resisting bending moment. “The bending moment increases from a minimum at section 4 to a maximum between sections 16 and 18, then gradually decreases almost uniformly to 0 near section 75.” “To resist bending moment stresses most effectively the material should be as far from the neutral axis as possible.” It is evident that the hollow shaft of the femur is an efficient structure for resisting bending moment stresses, all of the material in the shaft being relatively at a considerable distance from the neutral axis. It is evident that the hollow shaft provides efficiently for resisting bending moment not only due to the load on the femur-head, but from any other loads tending to produce bending in other planes. 38
3. Economy for resisting axial stress. 39
The inner architecture of the shaft is adapted to resist in the most efficient manner the combined action of the minimal shearing forces and the axial and maximum bending stresses. 40
The structure of the shaft is such as to secure great strength with a relatively small amount of material. 41

The Distal Portion of the Femur.—In frontal section (Fig. 249) in the distal 6 inches of the femur “there are to be seen two main systems of trabeculæ, a longitudinal and a transverse system. The trabeculæ of the former rise from the inner wall of the shaft and continue in perfectly straight lines parallel to the axis of the shaft and proceed to the epiphyseal line, whence they continue in more or less curved lines to meet the articular surface of the knee-joint at right angles at every point. Near the center there are a few thin, delicate, longitudinal trabeculæ which spring from the longitudinal trabeculæ just described, to which they are joined by fine transverse filaments that lie in planes parallel to the sagittal plane. 42
“The trabeculæ of the transverse system are somewhat lighter in structure than those of the longitudinal system, and consist of numerous trabeculæ at right angles to the latter. 43
“As the distal end of the femur is approached the shaft gradually becomes thinner until the articular surface is reached, where there remains only a thin shell of compact bone. With the gradual thinning of the compact bone of the shaft, there is a simultaneous increase in the amount of the spongy bone, and a gradual flaring of the femur which gives this portion of the bone a gradually increasing gross area of cross-section. 44
“There is a marked thickening of the shell of bone in the region of the intercondyloid fossa where the anterior and posterior crucial ligaments are attached. This thickened area is about 0.4 inch in diameter and consists of compact bone from which a number of thick trabeculæ pass at right angles to the main longitudinal system. The inner structure of the bone is here evidently adapted to the efficient distribution of the stresses arising from this ligamentary attachment. 45

FIG. 252– Plan of ossification of the femur. From five centers. (See enlarged image)

“Near the distal end of the femur the longitudinal trabeculæ gradually assume curved paths and end perpendicularly to the articular surface at every point. Such a structure is in accordance with the principles of mechanics, as stresses can be communicated through a frictionless joint only in a direction perpendicular to the joint surface at every point. 46
“With practically no increase in the amount of bony material used, there is a greatly increased stability produced by the expansion of the lower femur from a hollow shaft of compact bone to a structure of much larger cross-section almost entirely composed of spongy bone. 47

FIG. 253– Epiphysial lines of femur in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue. (See enlarged image)

FIG. 254– Epiphysial lines of femur in a young adult. Posterior aspect. The lines of attachment of the articular capsules are in blue. (See enlarged image)

“Significance of the Inner Architecture of the Distal Part of the Femur.—The function of the lower end of the femur is to transmit through a hinged joint the loads carried by the femur. For stability the width of the bearing on which the hinge action occurs should be relatively large. For economy of material the expansion of the end bearing should be as lightly constructed as is consistent with proper strength. In accordance with the principles of mechanics… …, the most efficient manner in which stresses are transmitted is by the arrangement of the resisting material in lines parallel to the direction in which the stresses occur and in the paths taken by the stresses. Theoretically the most efficient manner to attain these objects would be to prolong the innermost filaments of the bone as straight lines parallel to the longitudinal axis of the bone, and gradually to flare the outer shell of compact bone outward, and continuing to give off filaments of bone parallel to the longitudinal axis as the distal end of the femur is approached. These filaments should be well-braced transversely and each should carry its proportionate part of the total load, parallel to the longitudinal axis, transmitting it eventually to the articular surface, and in a direction perpendicular to that surface.” 48
Referring to Fig. 249, it is seen that the large expansion of the bone is produced by the gradual transition of the hollow shaft of compact bone to cancellated bone, resulting in the production of a much larger volume. The trabeculæ are given off from the shaft in lines parallel to the longitudinal axis, and are braced transversely by two series of trabeculæ at right angles to each other, in the same manner as required theoretically for economy. 49
Although the action of the muscles exerts an appreciable effect on the stresses in the femur, it is relatively small and very complex to analyze and has not been considered in the above analysis. 50

Ossification (Figs. 252, 253, 254).—The femur is ossified from five centers: one for the body, one for the head, one for each trochanter, and one for the lower extremity. Of all the long bones, except the clavicle, it is the first to show traces of ossification; this commences in the middle of the body, at about the seventh week of fetal life, and rapidly extends upward and downward. The centers in the epiphyses appear in the following order: in the lower end of the bone, at the ninth month of fetal life (from this center the condyles and epicondyles are formed); in the head, at the end of the first year after birth; in the greater trochanter, during the fourth year; and in the lesser trochanter, between the thirteenth and fourteenth years. The order in which the epiphyses are joined to the body is the reverse of that of their appearance; they are not united until after puberty, the lesser trochanter being first joined, then the greater, then the head, and, lastly, the inferior extremity, which is not united until the twentieth year. 51
Note 61. A cycloid is a curve traced by a point in the circumference of a wheel when the wheel is rolled along in a straight line. [back]
Note 62. The Laws of Bone Architecture. Am. Jour. of Anat., 21, 1917. The following paragraphs are taken almost verbatum from Koch’s article in which we have the first correct mathematical analysis of the femur in support of the theory of the functional form of bone proposed by Wolff and also by Roux. [back]

6c. 4. The Patella

(Knee Cap)

The patella (Figs. 255, 256) is a flat, triangular bone, situated on the front of the knee-joint. It is usually regarded as a sesamoid bone, developed in the tendon of the Quadriceps femoris, and resembles these bones (1) in being developed in a tendon; (2) in its center of ossification presenting a knotty or tuberculated outline; (3) in being composed mainly of dense cancellous tissue. It serves to protect the front of the joint, and increases the leverage of the Quadriceps femoris by making it act at a greater angle. It has an anterior and a posterior surface three borders, and an apex.

FIG. 255– Right patella. Anterior surface. (See enlarged image)

FIG. 256– Right patella. Posterior surface. (See enlarged image)

Surfaces.—The anterior surface is convex, perforated by small apertures for the passage of nutrient vessels, and marked by numerous rough, longitudinal striæ. This surface is covered, in the recent state, by an expansion from the tendon of the Quadriceps femoris, which is continuous below with the superficial fibers of the ligamentum patellæ. It is separated from the integument by a bursa. The posterior surface presents above a smooth, oval, articular area, divided into two facets by a vertical ridge; the ridge corresponds to the groove on the patellar surface of the femur, and the facets to the medial and lateral parts of the same surface; the lateral facet is the broader and deeper. Below the articular surface is a rough, convex, non-articular area, the lower half of which gives attachment to the ligamentum patellæ; the upper half is separated from the head of the tibia by adipose tissue. 2

Borders.—The base or superior border is thick, and sloped from behind, downward, and forward: it gives attachment to that portion of the Quadriceps femoris which is derived from the Rectus femoris and Vastus intermedius. The medial and lateral borders are thinner and converge below: they give attachment to those portions of the Quadriceps femoris which are derived from the Vasti lateralis and medialis.

Apex.—The apex is pointed, and gives attachment to the ligamentum patellæ.

Structure.—The patella consists of a nearly uniform dense cancellous tissue, covered by a thin compact lamina. The cancelli immediately beneath the anterior surface are arranged parallel with it. In the rest of the bone they radiate from the articular surface toward the other parts of the bone.

Ossification.—The patella is ossified from a single center, which usually makes its appearance in the second or third year, but may be delayed until the sixth year. More rarely, the bone is developed by two centers, placed side by side. Ossification is completed about the age of puberty.

Articulation.—The patella articulates with the femur.

6c. 5. The Tibia

(Shin Bone)

The tibia (Figs. 258, 259) is situated at the medial side of the leg, and, excepting the femur, is the longest bone of the skeleton. It is prismoid in form, expanded above, where it enters into the knee-joint, contracted in the lower third, and again enlarged but to a lesser extent below. In the male, its direction is vertical, and parallel with the bone of the opposite side; but in the female it has a slightly oblique direction downward and lateralward, to compensate for the greater obliquity of the femur. It has a body and two extremities.

FIG. 257– Upper surface of right tibia.

The Upper Extremity (proximal extremity).—The upper extremity is large, and expanded into two eminences, the medial and lateral condyles. The superior articular surface presents two smooth articular facets (Fig. 257). The medial facet, oval in shape, is slightly concave from side to side, and from before backward. The lateral, nearly circular, is concave from side to side, but slightly convex from before backward, especially at its posterior part, where it is prolonged on to the posterior surface for a short distance. The central portions of these facets articulate with the condyles of the femur, while their peripheral portions support the menisci of the knee-joint, which here intervene between the two bones. Between the articular facets, but nearer the posterior than the anterior aspect of the bone, is the intercondyloid eminence (spine of tibia), surmounted on either side by a prominent tubercle, on to the sides of which the articular facets are prolonged; in front of and behind the intercondyloid eminence are rough depressions for the attachment of the anterior and posterior cruciate ligaments and the menisci. The anterior surfaces of the condyles are continuous with one another, forming a large somewhat flattened area; this area is triangular, broad above, and perforated by large vascular foramina; narrow below where it ends in a large oblong elevation, the tuberosity of the tibia, which gives attachment to the ligamentum patellæ; a bursa intervenes between the deep surface of the ligament and the part of the bone immediately above the tuberosity. Posteriorly, the condyles are separated from each other by a shallow depression, the posterior intercondyloid fossa, which gives attachment to part of the posterior cruciate ligament of the knee-joint. The medial condyle presents posteriorly a deep transverse groove, for the insertion of the tendon of the Semimembranosus. Its medial surface is convex, rough, and prominent; it gives attachment to the tibial collateral ligament. The lateral condyle presents posteriorly a flat articular facet, nearly circular in form, directed downward, backward, and lateralward, for articulation with the head of the fibula. Its lateral surface is convex, rough, and prominent in front: on it is an eminence, situated on a level with the upper border of the tuberosity and at the junction of its anterior and lateral surfaces, for the attachment of the iliotibial band. Just below this a part of the Extensor digitorum longus takes origin and a slip from the tendon of the Biceps femoris is inserted. 2

The Body or Shaft (corpus tibiæ).—The body has three borders and three surfaces. 3

Borders.—The anterior crest or border, the most prominent of the three, commences above at the tuberosity, and ends below at the anterior margin of the medial malleolus. It is sinuous and prominent in the upper two-thirds of its extent, but smooth and rounded below; it gives attachment to the deep fascia of the leg. 4
The medial border is smooth and rounded above and below, but more prominent in the center; it begins at the back part of the medial condyle, and ends at the posterior border of the medial malleolus; its upper part gives attachment to the tibial collateral ligament of the knee-joint to the extent of about 5 cm., and insertion to some fibers of the Popliteus; from its middle third some fibers of the Soleus and Flexor digitorum longus take origin. 5
The interosseous crest or lateral border is thin and prominent, especially its central part, and gives attachment to the interosseous membrane; it commences above in front of the fibular articular facet, and bifurcates below, to form the boundaries of a triangular rough surface, for the attachment of the interosseous ligament connecting the tibia and fibula. 6

FIG. 258– Bones of the right leg. Anterior surface. (See enlarged image)

Surfaces.—The medial surface is smooth, convex, and broader above than below; its upper third, directed forward and medialward, is covered by the aponeurosis derived from the tendon of the Sartorius, and by the tendons of the Gracilis and Semitendinosus, all of which are inserted nearly as far forward as the anterior crest; in the rest of its extent it is subcutaneous. 7
The lateral surface is narrower than the medial; its upper two-thirds present a shallow groove for the origin of the Tibialis anterior; its lower third is smooth, convex, curves gradually forward to the anterior aspect of the bone, and is covered by the tendons of the Tibialis anterior, Extensor hallucis longus, and Extensor digitorum longus, arranged in this order from the medial side. 8

FIG. 259– Bones of the right leg. Posterior surface. (See enlarged image)

The posterior surface (Fig. 259) presents, at its upper part, a prominent ridge, the popliteal line, which extends obliquely downward from the back part of the articular facet for the fibula to the medial border, at the junction of its upper and middle thirds; it marks the lower limit of the insertion of the Popliteus, serves for the attachment of the fascia covering this muscle, and gives origin to part of the Soleus, Flexor digitorum longus, and Tibialis posterior. The triangular area, above this line, gives insertion to the Popliteus. The middle third of the posterior surface is divided by a vertical ridge into two parts; the ridge begins at the popliteal line and is well-marked above, but indistinct below; the medial and broader portion gives origin to the Flexor digitorum longus, the lateral and narrower to part of the Tibialis posterior. The remaining part of the posterior surface is smooth and covered by the Tibialis posterior, Flexor digitorum longus, and Flexor hallucis longus. Immediately below the popliteal line is the nutrient foramen, which is large and directed obliquely downward. 9

The Lower Extremity (distal extremity).—The lower extremity, much smaller than the upper, presents five surfaces; it is prolonged downward on its medial side as a strong process, the medial malleolus. 10

Surfaces.—The inferior articular surface is quadrilateral, and smooth for articulation with the talus. It is concave from before backward, broader in front than behind, and traversed from before backward by a slight elevation, separating two depressions. It is continuous with that on the medial malleolus. 11

FIG. 260– Plan of ossification of the tibia. From three centers. (See enlarged image)

FIG. 261– Epiphysial lines of tibia and fibula in a young adult. Anterior aspect. (See enlarged image)

The anterior surface of the lower extremity is smooth and rounded above, and covered by the tendons of the Extensor muscles; its lower margin presents a rough transverse depression for the attachment of the articular capsule of the ankle-joint. 12
The posterior surface is traversed by a shallow groove directed obliquely downward and medialward, continuous with a similar groove on the posterior surface of the talus and serving for the passage of the tendon of the Flexor hallucis longus. 13
The lateral surface presents a triangular rough depression for the attachment of the inferior interosseous ligament connecting it with the fibula; the lower part of this depression is smooth, covered with cartilage in the fresh state, and articulates with the fibula. The surface is bounded by two prominent borders, continuous above with the interosseous crest; they afford attachment to the anterior and posterior ligaments of the lateral malleolus. 14
The medial surface is prolonged downward to form a strong pyramidal process, flattened from without inward—the medial malleolus. The medial surface of this process is convex and subcutaneous; its lateral or articular surface is smooth and slightly concave, and articulates with the talus; its anterior border is rough, for the attachment of the anterior fibers of the deltoid ligament of the ankle-joint; its posterior border presents a broad groove, the malleolar sulcus, directed obliquely downward and medialward, and occasionally double; this sulcus lodges the tendons of the Tibialis posterior and Flexor digitorum longus. The summit of the medial malleolus is marked by a rough depression behind, for the attachment of the deltoid ligament. 15

Structure.—The structure of the tibia is like that of the other long bones. The compact wall of the body is thickest at the junction of the middle and lower thirds of the bone. 16

Ossification.—The tibia is ossified from three centers (Figs. 260, 261): one for the body and one for either extremity. Ossification begins in the center of the body, about the seventh week of fetal life, and gradually extends toward the extremities. The center for the upper epiphysis appears before or shortly after birth; it is flattened in form, and has a thin tongue-shaped process in front, which forms the tuberosity (Fig. 260); that for the lower epiphysis appears in the second year. The lower epiphysis joins the body at about the eighteenth, and the upper one joins about the twentieth year. Two additional centers occasionally exist, one for the tongue-shaped process of the upper epiphysis, which forms the tuberosity, and one for the medial malleolus. 17

6c. 6. The Fibula

(Calf Bone)

The fibula (Figs. 258, 259) is placed on the lateral side of the tibia, with which it is connected above and below. It is the smaller of the two bones, and, in proportion to its length, the most slender of all the long bones. Its upper extremity is small, placed toward the back of the head of the tibia, below the level of the knee-joint, and excluded from the formation of this joint. Its lower extremity inclines a little forward, so as to be on a plane anterior to that of the upper end; it projects below the tibia, and forms the lateral part of the ankle-joint. The bone has a body and two extremities.

The Upper Extremity or Head (capitulum fibulœ; proximal extremity).—The upper extremity is of an irregular quadrate form, presenting above a flattened articular surface, directed upward, forward, and medialward, for articulation with a corresponding surface on the lateral condyle of the tibia. On the lateral side is a thick and rough prominence continued behind into a pointed eminence, the apex (styloid process), which projects upward from the posterior part of the head. The prominence, at its upper and lateral part, gives attachment to the tendon of the Biceps femoris and to the fibular collateral ligament of the knee-joint, the ligament dividing the tendon into two parts. The remaining part of the circumference of the head is rough, for the attachment of muscles and ligaments. It presents in front a tubercle for the origin of the upper and anterior fibers of the Peronæus longus, and a surface for the attachment of the anterior ligament of the head; and behind, another tubercle, for the attachment of the posterior ligament of the head and the origin of the upper fibers of the Soleus.

The Body or Shaft (corpus fibulæ).—The body presents four borders—the antero-lateral, the antero-medial, the postero-lateral, and the postero-medial; and four surfaces—anterior, posterior, medial, and lateral. 3

Borders.—The antero-lateral border begins above in front of the head, runs vertically downward to a little below the middle of the bone, and then curving somewhat lateralward, bifurcates so as to embrace a triangular subcutaneous surface immediately above the lateral malleolus. This border gives attachment to an intermuscular septum, which separates the Extensor muscles on the anterior surface of the leg from the Peronæi longus and brevis on the lateral surface. 4
The antero-medial border, or interosseous crest, is situated close to the medial side of the preceding, and runs nearly parallel with it in the upper third of its extent, but diverges from it in the lower two-thirds. It begins above just beneath the head of the bone (sometimes it is quite indistinct for about 2.5 cm. below the head), and ends at the apex of a rough triangular surface immediately above the articular facet of the lateral malleolus. It serves for the attachment of the interosseous membrane, which separates the Extensor muscles in front from the Flexor muscles behind. 5
The postero-lateral border is prominent; it begins above at the apex, and ends below in the posterior border of the lateral malleolus. It is directed lateralward above, backward in the middle of its course, backward, and a little medialward below, and gives attachment to an aponeurosis which separates the Peronæi on the lateral surface from the Flexor muscles on the posterior surface. 6
The postero-medial border, sometimes called the oblique line, begins above at the medial side of the head, and ends by becoming continuous with the interosseous crest at the lower fourth of the bone. It is well-marked and prominent at the upper and middle parts of the bone. It gives attachment to an aponeurosis which separates the Tibialis posterior from the Soleus and Flexor hallucis longus. 7

FIG. 262– Lower extremity of right fibula. Medial aspect. (See enlarged image)

FIG. 263– Plan of ossification of the fibula. From three centers. (See enlarged image)

Surfaces.—The anterior surface is the interval between the antero-lateral and antero-medial borders. It is extremely narrow and flat in the upper third of its extent; broader and grooved longitudinally in its lower third; it serves for the origin of three muscles: the Extensor digitorum longus, Extensor hallucis longus, and Peronæus tertius. 8
The posterior surface is the space included between the postero-lateral and the postero-medial borders; it is continuous below with the triangular area above the articular surface of the lateral malleolus; it is directed backward above, backward and medialward at its middle, directly medialward below. Its upper third is rough, for the origin of the Soleus; its lower part presents a triangular surface, connected to the tibia by a strong interosseous ligament; the intervening part of the surface is covered by the fibers of origin of the Flexor hallucis longus. Near the middle of this surface is the nutrient foramen, which is directed downward. 9
The medial surface is the interval included between the antero-medial and the postero-medial borders. It is grooved for the origin of the Tibialis posterior. 10
The lateral surface is the space between the antero-lateral and postero-lateral borders. It is broad, and often deeply grooved; it is directed lateralward in the upper two-thirds of its course, backward in the lower third, where it is continuous with the posterior border of the lateral malleolus. This surface gives origin to the Peronæi longus and brevis. 11

The Lower Extremity or Lateral Malleolus (malleolus lateralis; distal extremity; external malleolus).—The lower extremity is of a pyramidal form, and somewhat flattened from side to side; it descends to a lower level than the medial malleolus. The lateral surface is convex, subcutaneous, and continuous with the triangular, subcutaneous surface on the lateral side of the body. The medial surface (Fig. 262) presents in front a smooth triangular surface, convex from above downward, which articulates with a corresponding surface on the lateral side of the talus. Behind and beneath the articular surface is a rough depression, which gives attachment to the posterior talofibular ligament. The anterior border is thick and rough, and marked below by a depression for the attachment of the anterior talofibular ligament. The posterior border is broad and presents the shallow malleolar sulcus, for the passage of the tendons of the Peronæi longus and brevis. The summit is rounded, and give attachment to the clacaneofibular ligament. 12

Ossification.—The fibula is ossified from three centers (Fig. 263): one for the body, and one for either end. Ossification begins in the body about the eighth week of fetal life, and extends toward the extremities. At birth the ends are cartilaginous. Ossification commences in the lower end in the second year, and in the upper about the fourth year. The lower epiphysis, the first to ossify, unites with the body about the twentieth year; the upper epiphysis joins about the twenty-fifth year. 13

FIG. 264– Left calcaneus, superior surface. (See enlarged image)

FIG. 265– Left calcaneus, inferior surface. (See enlarged image)

6d. The Foot. 1. The Tarsus

The skeleton of the foot (Figs. 268 and 269) consists of three parts: the tarsus, metatarsus, and phalanges. 1

The Tarsus (Ossa Tarsi)

The tarsal bones are seven in number, viz., the calcaneus, talus, cuboid, navicular, and the first, second, and third cuneiforms. 2

The Calcaneus (os calcis) (Figs. 264 to 267).—The calcaneus is the largest of the tarsal bones. It is situated at the lower and back part of the foot, serving to transmit the weight of the body to the ground, and forming a strong lever for the muscles of the calf. It is irregularly cuboidal in form, having its long axis directed forward and lateralward; it presents for examination six surfaces. 3

FIG. 266– Left calcaneus, lateral surface. (See enlarged image)

FIG. 267– Left calcaneus, medial surface. (See enlarged image)

Surfaces.—The superior surface extends behind on to that part of the bone which projects backward to form the heel. This varies in length in different individuals, is convex from side to side, concave from before backward, and supports a mass of fat placed in front of the tendo calcaneus. In front of this area is a large usually somewhat oval-shaped facet, the posterior articular surface, which looks upward and forward; it is convex from behind forward, and articulates with the posterior calcaneal facet on the under surface of the talus. It is bounded anteriorly by a deep depression which is continued backward and medialward in the form of a groove, the calcaneal sulcus. In the articulated foot this sulcus lies below a similar one on the under surface of the talus, and the two form a canal (sinus tarsi) for the lodgement of the interosseous talocalcaneal ligament. In front and to the medial side of this groove is an elongated facet, concave from behind forward, and with its long axis directed forward and lateralward. This facet is frequently divided into two by a notch: of the two, the posterior, and larger is termed the middle articular surface; it is supported on a projecting process of bone, the sustentaculum tali, and articulates with the middle calcaneal facet on the under surface of the talus; the anterior articular surface is placed on the anterior part of the body, and articulates with the anterior calcaneal facet on the talus. The upper surface, anterior and lateral to the facets, is rough for the attachment of ligaments and for the origin of the Extensor digitorum brevis. 4

FIG. 268– Bones of the right foot. Dorsal surface. (See enlarged image)

FIG. 269– Bones of the right foot. Plantar surface. (See enlarged image)

The inferior or plantar surface is uneven, wider behind than in front, and convex from side to side; it is bounded posteriorly by a transverse elevation, the calcaneal tuberosity, which is depressed in the middle and prolonged at either end into a process; the lateral process, small, prominent, and rounded, gives origin to part of the Abductor digiti quinti; the medial process, broader and larger, gives attachment, by its prominent medial margin, to the Abductor hallucis, and in front to the Flexor digitorum brevis and the plantar aponeurosis; the depression between the processes gives origin to the Abductor digiti quinti. The rough surface in front of the processes gives attachment to the long plantar ligament, and to the lateral head of the Quadratus plantæ while to a prominent tubercle nearer the anterior part of this surface, as well as to a transverse groove in front of the tubercle, is attached the plantar calcaneocuboid ligament. 5
The lateral surface is broad behind and narrow in front, flat and almost subcutaneous; near its center is a tubercle, for the attachment of the calcaneofibular ligament. At its upper and anterior part, this surface gives attachment to the lateral talocalcaneal ligament; and in front of the tubercle it presents a narrow surface marked by two oblique grooves. The grooves are separated by an elevated ridge, or tubercle, the trochlear process (peroneal tubercle), which varies much in size in different bones. The superior groove transmits the tendon of the Peronæus brevis; the inferior groove, that of the Peronæus longus. 6
The medial surface is deeply concave; it is directed obliquely downward and forward, and serves for the transmission of the plantar vessels and nerves into the sole of the foot; it affords origin to part of the Quadratus plantæ. At its upper and forepart is a horizontal eminence, the sustentaculum tali, which gives attachment to a slip of the tendon of the Tibialis posterior. This eminence is concave above, and articulates with the middle calcaneal articular surface of the talus; below, it is grooved for the tendon of the Flexor hallucis longus; its anterior margin gives attachment to the plantar calcaneonavicular ligament, and its medial, to a part of the deltoid ligament of the ankle-joint. 7
The anterior or cuboid articular surface is of a somewhat triangular form. It is concave from above downward and lateralward, and convex in a direction at right angles to this. Its medial border gives attachment to the plantar calcaneonavicular ligament. 8
The posterior surface is prominent, convex, wider below than above, and divisible into three areas. The lowest of these is rough, and covered by the fatty and fibrous tissue of the heel; the middle, also rough, gives insertion to the tendo calcaneus and Plantaris; while the highest is smooth, and is covered by a bursa which intervenes between it and the tendo calcaneus. 9

Articulations.—The calcaneus articulates with two bones: the talus and cuboid. 10

The Talus (astragalus; ankle bone) (Figs. 270 to 273).—The talus is the second largest of the tarsal bones. It occupies the middle and upper part of the tarsus, supporting the tibia above, resting upon the calcaneus below, articulating on either side with the malleoli, and in front with the navicular. It consists of a body, a neck, and a head 11

The Body (corpus tali).—The superior surface of the body presents, behind, a smooth trochlear surface, the trochlea, for articulation with the tibia. The trochlea is broader in front than behind, convex from before backward, slightly concave from side to side: in front it is continuous with the upper surface of the neck of the bone. 12

FIG. 270– Left talus, from above. (See enlarged image)

FIG. 271– Left talus, from below. (See enlarged image)

The inferior surface presents two articular areas, the posterior and middle calcaneal surfaces, separated from one another by a deep groove, the sulcus tali. The groove runs obliquely forward and lateralward, becoming gradually broader and deeper in front: in the articulated foot it lies above a similar groove upon the upper surface of the calcaneus, and forms, with it, a canal (sinus tarsi) filled up in the fresh state by the interosseous talocalcaneal ligament. The posterior calcaneal articular surface is large and of an oval or oblong form. It articulates with the corresponding facet on the upper surface of the calcaneus, 63 and is deeply concave in the direction of its long axis which runs forward and lateralward at an angle of about 45° with the median plane of the body. The middle calcaneal articular surface is small, oval in form and slightly convex; it articulates with the upper surface of the sustentaculum tali of the calcaneus. 13
The medial surface presents at its upper part a pear-shaped articular facet for the medial malleolus, continuous above with the trochlea; below the articular surface is a rough depression for the attachment of the deep portion of the deltoid ligament of the ankle-joint. 14

FIG. 272– Left talus, medial surface. (See enlarged image)

FIG. 273– Left talus, lateral surface. (See enlarged image)

The lateral surface carries a large triangular facet, concave from above downward, for articulation with the lateral malleolus; its anterior half is continuous above with the trochlea; and in front of it is a rough depression for the attachment of the anterior talofibular ligament. Between the posterior half of the lateral border of the trochlea and the posterior part of the base of the fibular articular surface is a triangular facet (Fawcett 64) which comes into contact with the transverse inferior tibiofibular ligament during flexion of the ankle-joint; below the base of this facet is a groove which affords attachment to the posterior talofibular ligament. 15
The posterior surface is narrow, and traversed by a groove running obliquely downward and medialward, and transmitting the tendon of the Flexor hallucis longus. Lateral to the groove is a prominent tubercle, the posterior process, to which the posterior talofibular ligament is attached; this process is sometimes separated from the rest of the talus, and is then known as the os trigonum. Medial to the groove is a second smaller tubercle. 16

The Neck (collum tali).—The neck is directed forward and medialward, and comprises the constricted portion of the bone between the body and the oval head. Its upper and medial surfaces are rough, for the attachment of ligaments; its lateral surface is concave and is continuous below with the deep groove for the interosseous talocalcaneal ligament. 17

The Head (caput tali).—The head looks forward and medialward; its anterior articular or navicular surface is large, oval, and convex. Its inferior surface has two facets, which are best seen in the fresh condition. The medial, situated in front of the middle calcaneal facet, is convex, triangular, or semi-oval in shape, and rests on the plantar calcaneonavicular ligament; the lateral, named the anterior calcaneal articular surface, is somewhat flattened, and articulates with the facet on the upper surface of the anterior part of the calcaneus. 18

Articulations.—The talus articulates with four bones: tibia, fibula, calcaneus, and navicular. 19

The Cuboid Bone (os cuboideum) (Figs. 274, 275).—The cuboid bone is placed on the lateral side of the foot, in front of the calcaneus, and behind the fourth and fifth metatarsal bones. It is of a pyramidal shape, its base being directed medialward. 20

FIG. 274– The left cuboid. Antero-medial view. (See enlarged image)

FIG. 275– The left cuboid. Postero-lateral view. (See enlarged image)

Surfaces.—The dorsal surface, directed upward and lateralward, is rough, for the attachment of ligaments. The plantar surface presents in front a deep groove, the peroneal sulcus, which runs obliquely forward and medialward; it lodges the tendon of the Peronæus longus, and is bounded behind by a prominent ridge, to which the long plantar ligament is attached. The ridge ends laterally in an eminence, the tuberosity, the surface of which presents an oval facet; on this facet glides the sesamoid bone or cartilage frequently found in the tendon of the Peronæus longus. The surface of bone behind the groove is rough, for the attachment of the plantar calcaneocuboid ligament, a few fibers of the Flexor hallucis brevis, and a fasciculus from the tendon of the Tibialis posterior. The lateral surface presents a deep notch formed by the commencement of the peroneal sulcus. The posterior surface is smooth, triangular, and concavo-convex, for articulation with the anterior surface of the calcaneus; its infero-medial angle projects backward as a process which underlies and supports the anterior end of the calcaneus. The anterior surface, of smaller size, but also irregularly triangular, is divided by a vertical ridge into two facets: the medial, quadrilateral in form, articulates with the fourth metatarsal; the lateral, larger and more triangular, articulates with the fifth. The medial surface is broad, irregularly quadrilateral, and presents at its middle and upper part a smooth oval facet, for articulation with the third cuneiform; and behind this (occasionally) a smaller facet, for articulation with the navicular; it is rough in the rest of its extent, for the attachment of strong interosseous ligaments. 21

Articulations.—The cuboid articulates with four bones: the calcaneus, third cuneiform, and fourth and fifth metatarsals; occasionally with a fifth, the navicular. 22

The Navicular Bone (os naviculare pedis; scaphoid bone) (Figs. 276, 277).—The navicular bone is situated at the medial side of the tarsus, between the talus behind and the cuneiform bones in front. 23

FIG. 276– The left navicular. Antero-lateral view. (See enlarged image)

FIG. 277– The left navicular. Postero-medial view. (See enlarged image)

Surfaces.—The anterior surface is convex from side to side, and subdivided by two ridges into three facets, for articulation with the three cuneiform bones. The posterior surface is oval, concave, broader laterally than medially, and articulates with the rounded head of the talus. The dorsal surface is convex from side to side, and rough for the attachment of ligaments. The plantar surface is irregular, and also rough for the attachment of ligaments. The medial surface presents a rounded tuberosity, the lower part of which gives attachment to part of the tendon of the Tibialis posterior. The lateral surface is rough and irregular for the attachment of ligaments, and occasionally presents a small facet for articulation with the cuboid bone. 24

Articulations.—The navicular articulates with four bones: the talus and the three cuneiforms; occasionally with a fifth, the cuboid. 25

The First Cuneiform Bone (os cuneiform primum; internalcuneiform) (Figs. 278, 279).—The first cuneiform bone is the largest of the three cuneiforms. It is situated at the medial side of the foot, between the navicular behind and the base of the first metatarsal in front. 26

FIG. 278– The left first cuneiform. Antero-medial view. (See enlarged image)

FIG. 279– The left first cuneiform. Postero-lateral view. (See enlarged image)

Surfaces.—The medial surface is subcutaneous, broad, and quadrilateral; at its anterior plantar angle is a smooth oval impression, into which part of the tendon of the Tibialis anterior is inserted; in the rest of its extent it is rough for the attachment of ligaments. The lateral surface is concave, presenting, along its superior and posterior borders a narrow L-shaped surface, the vertical limb and posterior part of the horizontal limb of which articulate with the second cuneiform, while the anterior part of the horizontal limb articulates with the second metatarsal bone: the rest of this surface is rough for the attachment of ligaments and part of the tendon of the Peronæus longus. The anterior surface, kidney-shaped and much larger than the posterior, articulates with the first metatarsal bone. The posterior surface is triangular, concave, and articulates with the most medial and largest of the three facets on the anterior surface of the navicular. The plantar surface is rough, and forms the base of the wedge; at its back part is a tuberosity for the insertion of part of the tendon of the Tibialis posterior. It also gives insertion in front to part of the tendon of the Tibialis anterior. The dorsal surface is the narrow end of the wedge, and is directed upward and lateralward; it is rough for the attachment of ligaments. 27

Articulations.—The first cuneiform articulates with four bones: the navicular, second cuneiform, and first and second metatarsals. 28

The Second Cuneiform Bone (os cuneiforme secundum; middle cuneiform) (Figs. 280, 281).—The second cuneiform bone, the smallest of the three, is of very regular wedge-like form, the thin end being directed downward. It is situated between the other two cuneiforms, and articulates with the navicular behind, and the second metatarsal in front. 29

Surfaces.—The anterior surface, triangular in form, and narrower than the posterior, articulates with the base of the second metatarsal bone. The posterior surface, also triangular, articulates with the intermediate facet on the anterior surface of the navicular. The medial surface carries an L-shaped articular facet, running along the superior and posterior borders, for articulation with the first cuneiform, and is rough in the rest of its extent for the attachment of ligaments. The lateral surface presents posteriorly a smooth facet for articulation with the third cuneiform bone. The dorsal surface forms the base of the wedge; it is quadrilateral and rough for the attachment of ligaments. The plantar surface, sharp and tuberculated, is also rough for the attachment of ligaments, and for the insertion of a slip from the tendon of the Tibialis posterior. 30

FIG. 280– The left second cuneiform. Antero-medial view. (See enlarged image)

FIG. 281– The left second cuneiform. Postero-lateral view. (See enlarged image)

Articulations.—The second cuneiform articulates with four bones: the navicular, first and third cuneiforms, and second metatarsal. 31

The Third Cuneiform Bone (os cuneiforme tertium; external cuneiform) (Figs. 282, 283).—The third cuneiform bone, intermediate in size between the two preceding, is wedge-shaped, the base being uppermost. It occupies the center of the front row of the tarsal bones, between the second cuneiform medially, the cuboid laterally, the navicular behind, and the third metatarsal in front. 32

Surfaces.—The anterior surface, triangular in form, articulates with the third metatarsal bone. The posterior surface articulates with the lateral facet on the anterior surface of the navicular, and is rough below for the attachment of ligamentous fibers. The medial surface presents an anterior and a posterior articular facet, separated by a rough depression: the anterior, sometimes divided, articulates with the lateral side of the base of the second metatarsal bone; the posterior skirts the posterior border, and articulates with the second cuneiform; the rough depression gives attachment to an interosseous ligament. The lateral surface also presents two articular facets, separated by a rough non-articular area; the anterior facet, situated at the superior angle of the bone, is small and semi-oval in shape, and articulates with the medial side of the base of the fourth metatarsal bone; the posterior and larger one is triangular or oval, and articulates with the cuboid; the rough, non-articular area serves for the attachment of an interosseous ligament. The three facets for articulation with the three metatarsal bones are continuous with one another; those for articulation with the second cuneiform and navicular are also continuous, but that for articulation with the cuboid is usually separate. The dorsal surface is of an oblong form, its postero-lateral angle being prolonged backward. The plantar surface is a rounded margin, and serves for the attachment of part of the tendon of the Tibialis posterior, part of the Flexor hallucis brevis, and ligaments. 33

Articulations.—The third cuneiform articulates with six bones: the navicular, second cuneiform, cuboid, and second, third, and fourth metatarsals. 34

FIG. 282– The left third cuneiform. Postero-medial view. (See enlarged image)

FIG. 283– The third left cuneiform. Antero-lateral view. (See enlarged image)

Note 63. Sewell (Journal of Anatomy and Physiology, vol. xxxviii) pointed out that in about 10 per cent. of bones a small triangular facet, continuous with the posterior calcaneal facet, is present at the junction of the lateral surface of the body with the posterior wall of the sulcus tali. [back]
Note 64. Edinburgh Medical Journal, 1895. [back]

6d. 2. The Metatarsus

The metatarsus consists of five bones which are numbered from the medial side (ossa metatarsalia I.-V.); each presents for examination a body and two extremities. 1

Common Characteristics of the Metatarsal Bones.—The body is prismoid in form, tapers gradually from the tarsal to the phalangeal extremity, and is curved longitudinally, so as to be concave below, slightly convex above. The base or posterior extremity is wedge-shaped, articulating proximally with the tarsal bones, and by its sides with the contiguous metatarsal bones: its dorsal and plantar surfaces are rough for the attachment of ligaments. The head or anterior extremity presents a convex articular surface, oblong from above downward, and extending farther backward below than above. Its sides are flattened, and on each is a depression, surmounted by a tubercle, for ligamentous attachment. Its plantar surface is grooved antero-posteriorly for the passage of the Flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface. 2

Characteristics of the Individual Metatarsal Bones. — The First Metatarsal Bone (os metatarsale I; metatarsal bone of the great toe) (Fig. 284).—The first metatarsal bone is remarkable for its great thickness, and is the shortest of the metatarsal bones. The body is strong, and of well-marked prismoid form. The base presents, as a rule, no articular facets on its sides, but occasionally on the lateral side there is an oval facet, by which it articulates with the second metatarsal. Its proximal articular surface is of large size and kidney-shaped; its circumference is grooved, for the tarsometatarsal ligaments, and medially gives insertion to part of the tendon of the Tibialis anterior; its plantar angle presents a rough oval prominence for the insertion of the tendon of the Peronæus longus. The head is large; on its plantar surface are two grooved facets, on which glide sesamoid bones; the facets are separated by a smooth elevation. 3

FIG. 284– The first metatarsal. (Left.) (See enlarged image)

FIG. 285– The second metatarsal. (Left.) (See enlarged image)

FIG. 286– The third metatarsal. (Left.) (See enlarged image)

FIG. 287– The fourth metatarsal. (Left.) (See enlarged image)

The Second Metatarsal Bone (os metatarsale II) (Fig. 285).—The second metatarsal bone is the longest of the metatarsal bones, being prolonged backward into the recess formed by the three cuneiform bones. Its base is broad above, narrow and rough below. It presents four articular surfaces: one behind, of a triangular form, for articulation with the second cuneiform; one at the upper part of its medial surface, for articulation with the first cuneiform; and two on its lateral surface, an upper and lower, separated by a rough non-articular interval. Each of these lateral articular surfaces is divided into two by a vertical ridge; the two anterior facets articulate with the third metatarsal; the two posterior (sometimes continuous) with the third cuneiform. A fifth facet is occasionally present for articulation with the first metatarsal; it is oval in shape, and is situated on the medial side of the body near the base. 4

The Third Metatarsal Bone (os metatarsale III) (Fig. 286).—The third metatarsal bone articulates proximally, by means of a triangular smooth surface, with the third cuneiform; medially, by two facets, with the second metatarsal; and laterally, by a single facet, with the fourth metatarsal. This last facet is situated at the dorsal angle of the base. 5

FIG. 288– The fifth metatarsal. (Left.) (See enlarged image)

The Fourth Metatarsal Bone (os metatarsale IV) (Fig. 287).—The fourth metatarsal bone is smaller in size than the preceding; its base presents an oblique quadrilateral surface for articulation with the cuboid; a smooth facet on the medial side, divided by a ridge into an anterior portion for articulation with the third metatarsal, and a posterior portion for articulation with the third cuneiform; on the lateral side a single facet, for articulation with the fifth metatarsal. 6

The Fifth Metatarsal Bone (os metatarsale V) (Fig. 288).—The fifth metatarsal bone is recognized by a rough eminence, the tuberosity, on the lateral side of its base. The base articulates behind, by a triangular surface cut obliquely in a transverse direction, with the cuboid; and medially, with the fourth metatarsal. On the medial part of its dorsal surface is inserted the tendon of the Peronæus tertius and on the dorsal surface of the tuberosity that of the Peronæus brevis. A strong band of the plantar aponeurosis connects the projecting part of the tuberosity with the lateral process of the tuberosity of the calcaneus. The plantar surface of the base is grooved for the tendon of the Abductor digiti quinti, and gives origin to the Flexor digiti quinti brevis. 7

Articulations.—The base of each metatarsal bone articulates with one or more of the tarsal bones, and the head with one of the first row of phalanges. The first metatarsal articulates with the first cuneiform, the second with all three cuneiforms, the third with the third cuneiform, the fourth with the third cuneiform and the cuboid, and the fifth with the cuboid. 8