5b. 9. The Hyoid Bone

(Os Hyoideum; Lingual Bone)

The hyoid bone is shaped like a horseshoe, and is suspended from the tips of the styloid processes of the temporal bones by the stylohyoid ligaments. It consists of five segments, viz., a body, two greater cornua, and two lesser cornua. 1

The Body or Basihyal (corpus oss. hyoidei).—The body or central part is of a quadrilateral form. Its anterior surface (Fig. 186) is convex and directed forward and upward. It is crossed in its upper half by a well-marked transverse ridge with a slight downward convexity, and in many cases a vertical median ridge divides it into two lateral halves. The portion of the vertical ridge above the transverse line is present in a majority of specimens, but the lower portion is evident only in rare cases. The anterior surface gives insertion to the Geniohyoideus in the greater part of its extent both above and below the transverse ridge; a portion of the origin of the Hyoglossus notches the lateral margin of the Geniohyoideus attachment. Below the transverse ridge the Mylohyoideus, Sternohyoideus, and Omohyoideus are inserted. The posterior surface is smooth, concave, directed backward and downward, and separated from the epiglottis by the hyothyroid membrane and a quantity of loose areolar tissue; a bursa intervenes between it and the hyothyroid membrane. The superior border is rounded, and gives attachment to the hyothyroid membrane and some aponeurotic fibers of the Genioglossus. The inferior border affords insertion medially to the Sternohyoideus and laterally to the Omohyoideus and occasionally a portion of the Thyreohyoideus. It also gives attachment to the Levator glandulæ thyreoideæ, when this muscle is present. In early life the lateral borders are connected to the greater cornua by synchondroses; after middle life usually by bony union.

FIG. 186– Hyoid bone. Anterior surface. Enlarged. (See enlarged image)

The Greater Cornua or Thyrohyals (cornua majora).—The greater cornua project backward from the lateral borders of the body; they are flattened from above downward and diminish in size from before backward; each ends in a tubercle to which is fixed the lateral hyothyroid ligament. The upper surface is rough close to its lateral border, for muscular attachments: the largest of these are the origins of the Hyoglossus and Constrictor pharyngis medius which extend along the whole length of the cornu; the Digastricus and Stylohyoideus have small insertions in front of these near the junction of the body with the cornu. To the medial border the hyothyroid membrane is attached, while the anterior half of the lateral border gives insertion to the Thyreohyoideus.

The Lesser Cornua or Ceratohyals (cornua minora).—The lesser cornu are two small, conical eminences, attached by their bases to the angles of junction between the body and greater cornua. They are connected to the body of the bone by fibrous tissue, and occasionally to the greater cornua by distinct diarthrodial joints, which usually persist throughout life, but occasionally become ankylosed.

The lesser cornua are situated in the line of the transverse ridge on the body and appear to be morphological continuations of it (Parsons 46). The apex of each cornu gives attachment to the stylohyoid ligament; 47 the Chondroglossus rises from the medial side of the base.

Ossification.—The hyoid is ossified from six centers: two for the body, and one for each cornu. Ossification commences in the greater cornua toward the end of fetal life, in the body shortly afterward, and in the lesser cornua during the first or second year after birth.

Note 46. See article on “The Topography and Morphology of the Human Hyoid Bone,” by F. G. Parsons, Journal of Anatomy and Physiology, vol. xliii. [back]
Note 47. These ligaments in many animals are distinct bones, and in man may undergo partial ossification. [back]

5c. The Exterior of the Skull

The skull as a whole may be viewed from different points, and the views so obtained are termed the normæ of the skull; thus, it may be examined from above (norma verticalis), from below (norma basalis), from the side (norma lateralis), from behind (norma occipitalis), or from the front (norma frontalis).

Norma Verticalis.—When viewed from above the outline presented varies greatly in different skulls; in some it is more or less oval, in others more nearly circular. The surface is traversed by three sutures, viz.: (1) the coronal sutures, nearly transverse is direction, between the frontal and parietals; (2) the sagittal sutures, medially placed, between the parietal bones, and deeply serrated in its anterior two-thirds; and (3) the upper part of the lambdoidal suture, between the parietals and the occipital. The point of junction of the sagittal and coronal suture is named the bregma, that of the sagittal and lambdoid sutures, the lambda; they indicate respectively the positions of the anterior and posterior fontanelles in the fetal skull. On either side of the sagittal suture are the parietal eminence and parietal foramen—the latter, however, is frequently absent on one or both sides. The skull is often somewhat flattened in the neighborhood of the parietal foramina, and the term obelion is applied to that point of the sagittal suture which is on a level with the foramina. In front is the glabella, and on its lateral aspects are the superciliary arches, and above these the frontal eminences. Immediately above the glabella may be seen the remains of the frontal suture; in a small percentage of skulls this suture persists and extends along the middle line to the bregma. Passing backward and upward from the zygomatic processes of the frontal bone are the temporal lines, which mark the upper limits of the temporal fossæ. The zygomatic arches may or may not be seen projecting beyond the anterior portions of these lines. 2

FIG. 187– Base of skull. Inferior surface. (See enlarged image)

Norma Basalis (Fig. 187).—The inferior surface of the base of the skull, exclusive of the mandible, is bounded in front by the incisor teeth in the maxillæ; behind, by the superior nuchal lines of the occipital; and laterally by the alveolar arch, the lower border of the zygomatic bone, the zygomatic arch and an imaginary line extending from it to the mastoid process and extremity of the superior nuchal line of the occipital. It is formed by the palatine processes of the maxillæ and palatine bones, the vomer, the pterygoid processes, the under surfaces of the great wings, spinous processes, and part of the body of the sphenoid, the under surfaces of the squamæ and mastoid and petrous portions of the temporals, and the under surface of the occipital bone. The anterior part or hard palate projects below the level of the rest of the surface, and is bounded in front and laterally by the alveolar arch containing the sixteen teeth of the maxillæ. Immediately behind the incisor teeth is the incisive foramen. In this foramen are two lateral apertures, the openings of the incisive canals (foramina of Stenson) which transmit the anterior branches of the descending palatine vessels, and the nasopalatine nerves. Occasionally two additional canals are present in the incisive foramen; they are termed the foramina of Scarpa and are situated in the middle line; when present they transmit the nasopalatine nerves. The vault of the hard palate is concave, uneven, perforated by numerous foramina, marked by depressions for the palatine glands, and traversed by a crucial suture formed by the junction of the four bones of which it is composed. In the young skull a suture may be seen extending on either side from the incisive foramen to the interval between the lateral incisor and canine teeth, and marking off the os incisivum or premaxillary bone. At either posterior angle of the hard palate is the greater palatine foramen, for the transmission of the descending palatine vessels and anterior palatine nerve; and running forward and medialward from it a groove, for the same vessels and nerve. Behind the posterior palatine foramen is the pyramidal process of the palatine bone, perforated by one or more lesser palatine foramina, and marked by the commencement of a transverse ridge, for the attachment of the tendinous expansion of the Tensor veli palatini. Projecting backward from the center of the posterior border of the hard palate is the posterior nasal spine, for the attachment of the Musculus uvulæ. Behind and above the hard palate are the choanæ, measuring about 2.5 cm. in their vertical and 1.25 cm. in their transverse diameters. They are separated from one another by the vomer, and each is bounded above by the body of the sphenoid, below by the horizontal part of the palatine bone, and laterally by the medial pterygoid plate of the sphenoid. At the superior border of the vomer may be seen the expanded alæ of this bone, receiving between them the rostrum of the sphenoid. Near the lateral margins of the alæ of the vomer, at the roots of the pterygoid processes, are the pharyngeal canals. The pterygoid process presents near its base the pterygoid canal, for the transmission of a nerve and artery. The medial pterygoid plate is long and narrow; on the lateral side of its base is the scaphoid fossa, for the origin of the Tensor veli palatini, and at its lower extremity the hamulus, around which the tendon of this muscle turns. The lateral pterygoid plate is broad; its lateral surface forms the medial boundary of the infratemporal fossa, and affords attachment to the Pterygoideus externus. 3
Behind the nasal cavities is the basilar portion of the occipital bone, presenting near its center the pharyngeal tubercle for the attachment of the fibrous raphé of the pharynx, with depressions on either side for the insertions of the Rectus capitis anterior and Longus capitis. At the base of the lateral pterygoid plate is the foramen ovale, for the transmission of the mandibular nerve, the accessory meningeal artery, and sometimes the lesser superficial petrosal nerve; behind this are the foramen spinosum which transmits the middle meningeal vessels, and the prominent spina angularis (sphenoidal spine), which gives attachment to the sphenomandibular ligament and the Tensor veli palatini. Lateral to the spina angularis is the mandibular fossa, divided into two parts by the petrotympanic fissure; the anterior portion, concave, smooth bounded in front by the articular tubercle, serves for the articulation of the condyle of the mandible; the posterior portion, rough and bounded behind by the tympanic part of the temporal, is sometimes occupied by a part of the parotid gland. Emerging from between the laminæ of the vaginal process of the tympanic part is the styloid process; and at the base of this process is the stylomastoid foramen, for the exit of the facial nerve, and entrance of the stylomastoid artery. Lateral to the stylomastoid foramen, between the tympanic part and the mastoid process, is the tympanomastoid fissure, for the auricular branch of the vagus. Upon the medial side of the mastoid process is the mastoid notch for the posterior belly of the Digastricus, and medial to the notch, the occipital groove for the occipital artery. At the base of the medial pterygoid plate is a large and somewhat triangular aperture, the foramen lacerum, bounded in front by the great wing of the sphenoid, behind by the apex of the petrous portion of the temporal bone, and medially by the body of the sphenoid and basilar portion of the occipital bone; it presents in front the posterior orifice of the pterygoid canal; behind, the aperture of the carotid canal. The lower part of this opening is filled up in the fresh state by a fibrocartilaginous plate, across the upper or cerebral surface of which the internal carotid artery passes. Lateral to this aperture is a groove, the sulcus tubæ auditivæ, between the petrous part of the temporal and the great wing of the sphenoid. This sulcus is directed lateralward and backward from the root of the medial pterygoid plate and lodges the cartilaginous part of the auditory tube; it is continuous behind with the canal in the temporal bone which forms the bony part of the same tube. At the bottom of this sulcus is a narrow cleft, the petrosphenoidal fissure, which is occupied, in the fresh condition, by a plate of cartilage. Behind this fissure is the under surface of the petrous portion of the temporal bone, presenting, near its apex, the quadrilateral rough surface, part of which affords attachment to the Levator veli palatini; lateral to this surface is the orifice of the carotid canal, and medial to it, the depression leading to the aquæductus cochleæ, the former transmitting the internal carotid artery and the carotid plexus of the sympathetic, the latter serving for the passage of a vein from the cochlea. Behind the carotid canal is the jugular foramen, a large aperture, formed in front by the petrous portion of the temporal, and behind by the occipital; it is generally larger on the right than on the left side, and may be subdivided into three compartments. The anterior compartment transmits the inferior petrosal sinus; the intermediate, the glossopharyngeal, vagus, and accessory nerves; the posterior, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries. On the ridge of bone dividing the carotid canal from the jugular foramen is the inferior tympanic canaliculus for the transmission of the tympanic branch of the glossopharyngeal nerve; and on the wall of the jugular foramen, near the root of the styloid process, is the mastoid canaliculus for the passage of the auricular branch of the vagus nerve. Extending forward from the jugular foramen to the foramen lacerum is the petroöccipital fissure occupied, in the fresh state, by a plate of cartilage. Behind the basilar portion of the occipital bone is the foramen magnum, bounded laterally by the occipital condyles, the medial sides of which are rough for the attachment of the alar ligaments. Lateral to each condyle is the jugular process which gives attachment to the Rectus capitis lateralis muscle and the lateral atlantoöccipital ligament. The foramen magnum transmits the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the ligaments connecting the occipital bone with the axis. The mid-points on the anterior and posterior margins of the foramen magnum are respectively termed the basion and the opisthion. In front of each condyle is the canal for the passage of the hypoglossal nerve and a meningeal artery. Behind each condyle is the condyloid fossa, perforated on one or both sides by the condyloid canal, for the transmission of a vein from the transverse sinus. Behind the foramen magnum is the median nuchal line ending above at the external occipital protuberance, while on either side are the superior and inferior nuchal lines; these, as well as the surfaces of bone between them, are rough for the attachment of the muscles which are enumerated on pages 129 and 130. 4

FIG. 188– Side view of the skull. (See enlarged image)

Norma Lateralis (Fig. 188).—When viewed from the side the skull is seen to consist of the cranium above and behind, and of the face below and in front. The cranium is somewhat ovoid in shape, but its contour varies in different cases and depends largely on the length and height of the skull and on the degree of prominence of the superciliary arches and frontal eminences. Entering into its formation are the frontal, the parietal, the occipital, the temporal, and the great wing of the sphenoid. These bones are joined to one another and to the zygomatic by the following sutures: the zygomaticotemporal between the zygomatic process of the temporal and the temporal process of the zygomatic; the zygomaticofrontal uniting the zygomatic bone with the zygomatic process of the frontal; the sutures surrounding the great wing of the sphenoid, viz., the sphenozygomatic in front, the sphenofrontal and sphenoparietal above, and the sphenosquamosal behind. The sphenoparietal suture varies in length in different skulls, and is absent in those cases where the frontal articulates with the temporal squama. The point corresponding with the posterior end of the sphenoparietal suture is named the pterion; it is situated about 3 cm. behind, and a little above the level of the zygomatic process of the frontal bone. 5
The squamosal suture arches backward from the pterion and connects the temporal squama with the lower border of the parietal: this suture is continuous behind with the short, nearly horizontal parietomastoid suture, which unites the mastoid process of the temporal with the region of the mastoid angle of the parietal. Extending from above downward and forward across the cranium are the coronal and lambdoidal sutures; the former connects the parietals with the frontal, the latter, the parietals with the occipital. The lambdoidal suture is continuous below with the occipitomastoid suture between the occipital and the mastoid portion of the temporal. In or near the last suture is the mastoid foramen, for the transmission of an emissary vein. The point of meeting of the parietomastoid, occipitomastoid, and lambdoidal sutures is known as the asterion. Immediately above the orbital margin is the superciliary arch, and, at a higher level, the frontal eminence. Near the center of the parietal bone is the parietal eminence. Posteriorly is the external occipital protuberance, from which the superior nuchal line may be followed forward to the mastoid process. Arching across the side of the cranium are the temporal lines, which mark the upper limit of the temporal fossa. 6

The Temporal Fossa (fossa temporalis).—The temporal fossa is bounded above and behind by the temporal lines, which extend from the zygomatic process of the frontal bone upward and backward across the frontal and parietal bones, and then curve downward and forward to become continuous with the supramastoid crest and the posterior root of the zygomatic arch. The point where the upper temporal line cuts the coronal suture is named the stephanion. The temporal fossa is bounded in front by the frontal and zygomatic bones, and opening on the back of the latter is the zygomaticotemporal foramen. Laterally the fossa is limited by the zygomatic arch, formed by the zygomatic and temporal bones; below, it is separated from the infratemporal fossa by the infratemporal crest on the great wing of the sphenoid, and by a ridge, continuous with this crest, which is carried backward across the temporal squama to the anterior root of the zygomatic process. In front and below, the fossa communicates with the orbital cavity through the inferior orbital or sphenomaxillary fissure. The floor of the fossa is deeply concave in front and convex behind, and is formed by the zygomatic, frontal, parietal, sphenoid, and temporal bones. It is traversed by vascular furrows; one, usually well-marked, runs upward above and in front of the external acoustic meatus, and lodges the middle temporal artery. Two others, frequently indistinct, may be observed on the anterior part of the floor, and are for the anterior and posterior deep temporal arteries. The temporal fossa contains the Temporalis muscle and its vessels and nerves, together with the zygomaticotemporal nerve. 7
The zygomatic arch is formed by the zygomatic process of the temporal and the temporal process of the zygomatic, the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process of the mandible. The zygomatic process of the temporal arises by two roots, an anterior, directed inward in front of the mandibular fossa, where it expands to form the articular tubercle, and a posterior, which runs backward above the external acoustic meatus and is continuous with the supramastoid crest. The upper border of the arch gives attachment to the temporal fascia; the lower border and medial surface give origin to the Masseter. 8
Below the posterior root of the zygomatic arch is the elliptical orifice of the external acoustic meatus, bounded in front, below, and behind by the tympanic part of the temporal bone; to its outer margin the cartilaginous segment of the external acoustic meatus is attached. The small triangular area between the posterior root of the zygomatic arch and the postero-superior part of the orifice is termed the suprameatal triangle, on the anterior border of which a small spinous process, the suprameatal spine, is sometimes seen. Between the tympanic part and the articular tubercle is the mandibular fossa, divided into two parts by the petrotympanic fissure. The anterior and larger part of the fossa articulates with the condyle of the mandible and is limited behind by the external acoustic meatus: the posterior part sometimes lodges a portion of the parotid gland. The styloid process extends downward and forward for a variable distance from the lower part of the tympanic part, and gives attachment to the Styloglossus, Stylohyoideus, and Stylopharyngeus, and to the stylohyoid and stylomandibular ligaments. Projecting downward behind the external acoustic meatus is the mastoid process, to the outer surface of which the Sternocleidomastoideus, Splenius capitis, and Longissimus capitis are attached. 9

FIG. 189– Left infratemporal fossa. (See enlarged image)

The Infratemporal Fossa (fossa infratemporalis; zygomatic fossa) (Fig. 189).—The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch. It is bounded, in front, by the infratemporal surface of the maxilla and the ridge which descends from its zygomatic process; behind, by the articular tubercle of the temporal and the spinal angularis of the sphenoid; above, by the great wing of the sphenoid below the infratemporal crest, and by the under surface of the temporal squama; below, by the alveolar border of the maxilla; medially, by the lateral pterygoid plate. It contains the lower part of the Temporalis, the Pterygoidei internus and externus, the internal maxillary vessels, and the mandibular and maxillary nerves. The foramen ovale and foramen spinosum open on its roof, and the alveolar canals on its anterior wall. At its upper and medial part are two fissures, which together form a T-shaped fissure, the horizontal limb being named the inferior orbital, and the vertical one the pterygomaxillary. 10
The inferior orbital fissure (fissura orbitalis inferior; sphenomaxillary fissure), horizontal in direction, opens into the lateral and back part of the orbit. It is bounded above by the lower border of the orbital surface of the great wing of the sphenoid; below, by the lateral border of the orbital surface of the maxilla and the orbital process of the palatine bone; laterally, by a small part of the zygomatic bone: 48 medially, it joins at right angles with the pterygomaxillary fissure. Through the inferior orbital fissure the orbit communicates with the temporal, infratemporal, and pterygopalatine fossæ; the fissure transmits the maxillary nerve and its zygomatic branch, the infraorbital vessels, the ascending branches from the sphenopalatine ganglion, and a vein which connects the inferior ophthalmic vein with the pterygoid venous plexus. 11
The pterygomaxillary fissure is vertical, and descends at right angles from the medial end of the preceding; it is a triangular interval, formed by the divergence of the maxilla from the pterygoid process of the sphenoid. It connects the infratemporal with the pterygopalatine fossa, and transmits the terminal part of the internal maxillary artery. 12

The Pterygopalatine Fossa (fossa pterygopalatina; sphenomaxillary fossa).—The pterygopalatine fossa is a small, triangular space at the angle of junction of the inferior orbital and pterygomaxillary fissures, and placed beneath the apex of the orbit. It is bounded above by the under surface of the body of the sphenoid and by the orbital process of the palatine bone; in front, by the infratemporal surface of the maxilla; behind, by the base of the pterygoid process and lower part of the anterior surface of the great wing of the sphenoid; medially, by the vertical part of the palatine bone with its orbital and sphenoidal processes. This fossa communicates with the orbit by the inferior orbital fissure, with the nasal cavity by the sphenopalatine foramen, and with the infratemporal fossa by the pterygomaxillary fissure. Five foramina open into it. Of these, three are on the posterior wall, viz., the foramen rotundum, the pterygoid canal, and the pharyngeal canal, in this order downward and medialward. On the medial wall is the sphenopalatine foramen, and below is the superior orifice of the pterygopalatine canal. The fossa contains the maxillary nerve, the sphenopalatine ganglion, and the terminal part of the internal maxillary artery. 13

Norma Occipitalis.—When viewed from behind the cranium presents a more or less circular outline. In the middle line is the posterior part of the sagittal suture connecting the parietal bones; extending downward and lateralward from the hinder end of the sagittal suture is the deeply serrated lambdoidal suture joining the parietals to the occipital and continuous below with the parietomastoid and occipitomastoid sutures; it frequently contains one or more sutural bones. Near the middle of the occipital squama is the external occipital protuberance or inion, and extending lateralward from it on either side is the superior nuchal line, and above this the faintly marked highest nuchal line. The part of the squama above the inion and highest lines is named the planum occipitale, and is covered by the Occipitalis muscle; the part below is termed the planum nuchale, and is divided by the median nuchal line which runs downward and forward from the inion to the foramen magnum; this ridge gives attachment to the ligamentum nuchæ. The muscles attached to the planum nuchale are enumerated on p. 130. Below and in front are the mastoid processes, convex laterally and grooved medially by the mastoid notches. In or near the occipitomastoid suture is the mastoid foramen for the passage of the mastoid emissary vein. 14

Norma Frontalis (Fig. 190).—When viewed from the front the skull exhibits a somewhat oval outline, limited above by the frontal bone, below by the body of the mandible, and laterally by the zygomatic bones and the mandibular rami. The upper part, formed by the frontal squama, is smooth and convex. The lower part, made up of the bones of the face, is irregular; it is excavated laterally by the orbital cavities, and presents in the middle line the anterior nasal aperture leading to the nasal cavities, and below this the transverse slit between the upper and lower dental arcades. Above, the frontal eminences stand out more or less prominently, and beneath these are the superciliary arches, joined to one another in the middle by the glabella. On and above the glabella a trace of the frontal suture sometimes persists; beneath it is the frontonasal suture, the mid-point of which is termed the nasion. Behind and below the frontonasal suture the frontal articulates with the frontal process of the maxilla and with the lacrimal. Arching transversely below the superciliary arches is the upper part of the margin of the orbit, thin and prominent in its lateral two-thirds, rounded in its medial third, and presenting, at the junction of these two portions, the supraorbital notch or foramen for the supraorbital nerve and vessels. The supraorbital margin ends laterally in the zygomatic process which articulates with the zygomatic bone, and from it the temporal line extends upward and backward. Below the frontonasal suture is the bridge of the nose, convex from side to side, concavo-convex from above downward, and formed by the two nasal bones supported in the middle line by the perpendicular plate of the ethmoid, and laterally by the frontal processes of the maxillæ which are prolonged upward between the nasal and lacrimal bones and form the lower and medial part of the circumference of each orbit. Below the nasal bones and between the maxillæ is the anterior aperture of the nose, pyriform in shape, with the narrow end directed upward. Laterally this opening is bounded by sharp margins, to which the lateral and alar cartilages of the nose are attached; below, the margins are thicker and curve medialward and forward to end in the anterior nasal spine. On looking into the nasal cavity, the bony septum which separates the nasal cavities presents, in front, a large triangular deficiency; this, in the fresh state, is filled up by the cartilage of the nasal septum; on the lateral wall of each nasal cavity the anterior part of the inferior nasal concha is visible. Below and lateral to the anterior nasal aperture are the anterior surfaces of the maxillæ, each perforated, near the lower margin of the orbit, by the infraorbital foramen for the passage of the infraorbital nerve and vessels. Below and medial to this foramen is the canine eminence separating the incisive from the canine fossa. Beneath these fossæ are the alveolar processes of the maxillæ containing the upper teeth, which overlap the teeth of the mandible in front. The zygomatic bone on either side forms the prominence of the cheek, the lower and lateral portion of the orbital cavity, and the anterior part of the zygomatic arch. It articulates medially with the maxilla, behind with the zygomatic process of the temporal, and above with the great wing of the sphenoid and the zygomatic process of the frontal; it is perforated by the zygomaticofacial foramen for the passage of the zygomaticofacial nerve. On the body of the mandible is a median ridge, indicating the position of the symphysis; this ridge divides below to enclose the mental protuberance, the lateral angles of which constitute the mental tubercles. Below the incisor teeth is the incisive fossa, and beneath the second premolar tooth the mental foramen which transmits the mental nerve and vessels. The oblique line runs upward from the mental tubercle and is continuous behind with the anterior border of the ramus. The posterior border of the ramus runs downward and forward from the condyle to the angle, which is frequently more or less everted. 15

FIG. 190– The skull from the front. (See enlarged image)

FIG. 191– Horizontal section of nasal and orbital cavities. (See enlarged image)

The Orbits (orbitæ) (Fig. 190).—The orbits are two quadrilateral pyramidal cavities, situated at the upper and anterior part of the face, their bases being directed forward and lateralward, and their apices backward and medialward, so that their long axes, if continued backward, would meet over the body of the sphenoid. Each presents for examination a roof, a floor, a medial and a lateral wall, a base, and an apex. 16

FIG. 192– Medial wall of left orbit. (See enlarged image)

The roof is concave, directed downward, and slightly forward, and formed in front by the orbital plate of the frontal; behind by the small wing of the sphenoid. It presents medially the trochlear fovea for the attachment of the cartilaginous pulley of the Obliquus oculi superior; laterally, the lacrimal fossa for the lacrimal gland; and posteriorly, the suture between the frontal bone and the small wing of the sphenoid. 17
The floor is directed upward and lateralward, and is of less extent than the roof; it is formed chiefly by the orbital surface of the maxilla; in front and laterally, by the orbital process of the zygomatic bone, and behind and medially, to a small extent, by the orbital process of the palatine. At its medial angle is the upper opening of the nasolacrimal canal, immediately to the lateral side of which is a depression for the origin of the Obliquus oculi inferior. On its lateral part is the suture between the maxilla and zygomatic bone, and at its posterior part that between the maxilla and the orbital process of the palatine. Running forward near the middle of the floor is the infraorbital groove, ending in front in the infraorbital canal and transmitting the infraorbital nerve and vessels. 18
The medial wall (Fig. 192) is nearly vertical, and is formed from before backward by the frontal process of the maxilla, the lacrimal, the lamina papyracea of the ethmoid, and a small part of the body of the sphenoid in front of the optic foramen. Sometimes the sphenoidal concha forms a small part of this wall (see page 152). It exhibits three vertical sutures, viz., the lacrimomaxillary, lacrimoethmoidal, and sphenoethmoidal. In front is seen the lacrimal groove, which lodges the lacrimal sac, and behind the groove is the posterior lacrimal crest, from which the lacrimal part of the Orbicularis oculi arises. At the junction of the medial wall and the roof are the frontomaxillary, frontolacrimal, frontoethmoidal, and sphenofrontal sutures. The point of junction of the anterior border of the lacrimal with the frontal is named the dacryon. In the frontoethmoidal suture are the anterior and posterior ethmoidal foramina, the former transmitting the nasociliary nerve and anterior ethmoidal vessels, the latter the posterior ethmoidal nerve and vessels. 19
The lateral wall, directed medialward and forward, is formed by the orbital process of the zygomatic and the orbital surface of the great wing of the sphenoid; these are united by the sphenozygomatic suture which terminates below at the front end of the inferior orbital fissure. On the orbital process of the zygomatic bone are the orbital tubercle (Whitnall) and the orifices of one or two canals which transmit the branches of the zygomatic nerve. Between the roof and the lateral wall, near the apex of the orbit, is the superior orbital fissure. Through this fissure the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the abducent nerves enter the orbital cavity, also some filaments from the cavernous plexus of the sympathetic and the orbital branches of the middle meningeal artery. Passing backward through the fissure are the ophthalmic vein and the recurrent branch from the lacrimal artery to the dura mater. The lateral wall and the floor are separated posteriorly by the inferior orbital fissure which transmits the maxillary nerve and its zygomatic branch, the infraorbital vessels, and the ascending branches from the sphenopalatine ganglion. 20
The base of the orbit, quadrilateral in shape, is formed above by the supraorbital arch of the frontal bone, in which is the supraorbital notch or foramen for the passage of the supraorbital vessels and nerve; below by the zygomatic bone and maxilla, united by the zygomaticomaxillary suture; laterally by the zygomatic bone and the zygomatic process of the frontal joined by the zygomaticofrontal suture; medially by the frontal bone and the frontal process of the maxilla united by the frontomaxillary suture. 21
The apex, situated at the back of the orbit, corresponds to the optic foramen 49 a short, cylindrical canal, which transmits the optic nerve and ophthalmic artery. 22
It will thus be seen that there are nine openings communicating with each orbit, viz., the optic foramen, superior and inferior orbital fissures, supraorbital foramen, infraorbital canal, anterior and posterior ethmoidal foramina, zygomatic foramen, and the canal for the nasolacrimal duct. 23
Note 48. Occasionally the maxilla and the sphenoid articulate with each other at the anterior extremity of this fissure; the zygomatic is then excluded from it. [back]
Note 49. Some anatomists describe the apex of the orbit as corresponding with the medial end of the superior orbital fissure. It seems better, however, to adopt the statement in the text, since the ocular muscles take origin around the optic foramen, and diverge from it to the bulb of the eye. [back]

5d. The Interior of the Skull

Inner Surface of the Skull-cap.—The inner surface of the skull-cap is concave and presents depressions for the convolutions of the cerebrum, together with numerous furrows for the lodgement of branches of the meningeal vessels. Along the middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its margins afford attachment to the falx cerebri. On either side of it are several depressions for the arachnoid granulations, and at its back part, the openings of the parietal foramina when these are present. It is crossed, in front, by the coronal suture, and behind by the lambdoidal, while the sagittal lies in the medial plane between the parietal bones. 1

Upper Surface of the Base of the Skull (Fig. 193).—The upper surface of the base of the skull or floor of the cranial cavity presents three fossæ, called the anterior, middle, and posterior cranial fossæ. 2

Anterior Fossa (fossa cranii anterior).—The floor of the anterior fossa is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the small wings and front part of the body of the sphenoid; it is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. It is traversed by the frontoethmoidal, sphenoethmoidal, and sphenofrontal sutures. Its lateral portions roof in the orbital cavities and support the frontal lobes of the cerebrum; they are convex and marked by depressions for the brain convolutions, and grooves for branches of the meningeal vessels. The central portion corresponds with the roof of the nasal cavity, and is markedly depressed on either side of the crista galli. It presents, in and near the median line, from before backward, the commencement of the frontal crest for the attachment of the falx cerebri; the foramen cecum, between the frontal bone and the crista galli of the ethmoid, which usually transmits a small vein from the nasal cavity to the superior sagittal sinus; behind the foramen cecum, the crista galli, the free margin of which affords attachment to the falx cerebri; on either side of the crista galli, the olfactory groove formed by the cribriform plate, which supports the olfactory bulb and presents foramina for the transmission of the olfactory nerves, and in front a slit-like opening for the nasociliary nerve. Lateral to either olfactory groove are the internal openings of the anterior and posterior ethmoidal foramina; the anterior, situated about the middle of the lateral margin of the olfactory groove, transmits the anterior ethmoidal vessels and the nasociliary nerve; the nerve runs in a groove along the lateral edge of the cribriform plate to the slit-like opening above mentioned; the posterior ethmoidal foramen opens at the back part of this margin under cover of the projecting lamina of the sphenoid, and transmits the posterior ethmoidal vessels and nerve. Farther back in the middle line is the ethmoidal spine, bounded behind by a slight elevation separating two shallow longitudinal grooves which support the olfactory lobes. Behind this is the anterior margin of the chiasmatic groove, running lateralward on either side to the upper margin of the optic foramen. 3

The Middle Fossa (fossa cranii media).—The middle fossa, deeper than the preceding, is narrow in the middle, and wide at the sides of the skull. It is bounded in front by the posterior margins of the small wings of the sphenoid, the anterior clinoid processes, and the ridge forming the anterior margin of the chiasmatic groove; behind, by the superior angles of the petrous portions of the temporals and the dorsum sellæ; laterally by the temporal squamæ, sphenoidal angles of the parietals, and great wings of the sphenoid. It is traversed by the squamosal, sphenoparietal, sphenosquamosal, and sphenopetrosal sutures. 4
The middle part of the fossa presents, in front, the chiasmatic groove and tuberculum sellæ; the chiasmatic groove ends on either side at the optic foramen, which transmits the optic nerve and ophthalmic artery to the orbital cavity. Behind the optic foramen the anterior clinoid process is directed backward and medialward and gives attachment to the tentorium cerebelli. Behind the tuberculum sellæ is a deep depression, the sella turcica, containing the fossa hypophyseos, which lodges the hypophysis, and presents on its anterior wall the middle clinoid processes. The sella turcica is bounded posteriorly by a quadrilateral plate of bone, the dorsum sellæ, the upper angles of which are surmounted by the posterior clinoid processes: these afford attachment to the tentorium cerebelli, and below each is a notch for the abducent nerve. On either side of the sella turcica is the carotid groove, which is broad, shallow, and curved somewhat like the italic letter f. It begins behind at the foramen lacerum, and ends on the medial side of the anterior clinoid process, where it is sometimes converted into a foramen (carotico-clinoid) by the union of the anterior with the middle clinoid process; posteriorly, it is bounded laterally by the lingula. This groove lodges the cavernous sinus and the internal carotid artery, the latter being surrounded by a plexus of sympathetic nerves. 5

FIG. 193– Base of the skull. Upper surface. (See enlarged image)

The lateral parts of the middle fossa are of considerable depth, and support the temporal lobes of the brain. They are marked by depressions for the brain convolutions and traversed by furrows for the anterior and posterior branches of the middle meningeal vessels. These furrows begin near the foramen spinosum, and the anterior runs forward and upward to the sphenoidal angle of the parietal, where it is sometimes converted into a bony canal; the posterior runs lateralward and backward across the temporal squama and passes on to the parietal near the middle of its lower border. The following apertures are also to be seen. In front is the superior orbital fissure, bounded above by the small wing, below, by the great wing, and medially, by the body of the sphenoid; it is usually completed laterally by the orbital plate of the frontal bone. It transmits to the orbital cavity the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the abducent nerves, some filaments from the cavernous plexus of the sympathetic, and the orbital branch of the middle meningeal artery; and from the orbital cavity a recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic veins. Behind the medial end of the superior orbital fissure is the foramen rotundum, for the passage of the maxillary nerve. Behind and lateral to the foramen rotundum is the foramen ovale, which transmits the mandibular nerve, the accessory meningeal artery, and the lesser superficial petrosal nerve. 50 Medial to the foramen ovale is the foramen Vesalii, which varies in size in different individuals, and is often absent; when present, it opens below at the lateral side of the scaphoid fossa, and transmits a small vein. Lateral to the foramen ovale is the foramen spinosum, for the passage of the middle meningeal vessels, and a recurrent branch from the mandibular nerve. Medial to the foramen ovale is the foramen lacerum; in the fresh state the lower part of this aperture is filled up by a layer of fibrocartilage, while its upper and inner parts transmit the internal carotid artery surrounded by a plexus of sympathetic nerves. The nerve of the pterygoid canal and a meningeal branch from the ascending pharyngeal artery pierce the layer of fibrocartilage. On the anterior surface of the petrous portion of the temporal bone are seen the eminence caused by the projection of the superior semicircular canal; in front of and a little lateral to this a depression corresponding to the roof of the tympanic cavity; the groove leading to the hiatus of the facial canal, for the transmission of the greater superficial petrosal nerve and the petrosal branch of the middle meningeal artery; beneath it, the smaller groove, for the passage of the lesser superficial petrosal nerve; and, near the apex of the bone, the depression for the semilunar ganglion and the orifice of the carotid canal. 6

The Posterior Fossa (fossa cranii posterior).—The posterior fossa is the largest and deepest of the three. It is formed by the dorsum sellæ and clivus of the sphenoid, the occipital, the petrous and mastoid portions of the temporals, and the mastoid angles of the parietal bones; it is crossed by the occipitomastoid and the parietomastoid sutures, and lodges the cerebellum, pons, and medulla oblongata. It is separated from the middle fossa in and near the median line by the dorsum sellæ of the sphenoid and on either side by the superior angle of the petrous portion of the temporal bone. This angle gives attachment to the tentorum cerebelli, is grooved for the superior petrosal sinus, and presents at its medial end a notch upon which the trigeminal nerve rests. The fossa is limited behind by the grooves for the transverse sinuses. In its center is the foramen magnum, on either side of which is a rough tubercle for the attachment of the alar ligaments; a little above this tubercle is the canal, which transmits the hypoglossal nerve and a meningeal branch from the ascending pharyngeal artery. In front of the foramen magnum the basilar portion of the occipital and the posterior part of the body of the sphenoid form a grooved surface which supports the medulla oblongata and pons; in the young skull these bones are joined by a synchondrosis. This grooved surface is separated on either side from the petrous portion of the temporal by the petro-occipital fissure, which is occupied in the fresh state by a plate of cartilage; the fissure is continuous behind with the jugular foramen, and its margins are grooved for the inferior petrosal sinus. The jugular foramen is situated between the lateral part of the occipital and the petrous part of the temporal. The anterior portion of this foramen transmits the inferior petrosal sinus; the posterior portion, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries; and the intermediate portion, the glossopharyngeal, vagus, and accessory nerves. Above the jugular foramen is the internal acoustic meatus, for the facial and acoustic nerves and internal auditory artery; behind and lateral to this is the slit-like opening leading into the aquæductus vestibuli, which lodges the ductus endolymphaticus; while between these, and near the superior angle of the petrous portion, is a small triangular depression, the remains of the fossa subarcuata, which lodges a process of the dura mater and occasionally transmits a small vein. Behind the foramen magnum are the inferior occipital fossæ, which support the hemispheres of the cerebellum, separated from one another by the internal occipital crest, which serves for the attachment of the falx cerebelli, and lodges the occipital sinus. The posterior fossæ are surmounted by the deep grooves for the transverse sinuses. Each of these channels, in its passage to the jugular foramen, grooves the occipital, the mastoid angle of the parietal, the mastoid portion of the temporal, and the jugular process of the occipital, and ends at the back part of the jugular foramen. Where this sinus grooves the mastoid portion of the temporal, the orifice of the mastoid foramen may be seen; and, just previous to its termination, the condyloid canal opens into it; neither opening is constant. 7

FIG. 194– Sagittal section of skull. (See enlarged image)

The Nasal Cavity (cavum nasi; nasal fossa).—The nasal cavities are two irregular spaces, situated one on either side of the middle line of the face, extending from the base of the cranium to the roof of the mouth, and separated from each other by a thin vertical septum. They open on the face through the pear-shaped anterior nasal aperture, and their posterior openings or choanæ communicate, in the fresh state, with the nasal part of the pharynx. They are much narrower above than below, and in the middle than at their anterior or posterior openings: their depth, which is considerable, is greatest in the middle. They communicate with the frontal, ethmoidal, sphenoidal, and maxillary sinuses. Each cavity is bounded by a roof, a floor, a medial and a lateral wall. 8
The roof (Figs. 195, 196) is horizontal in its central part, but slopes downward in front and behind; it is formed in front by the nasal bone and the spine of the frontal; in the middle, by the cribriform plate of the ethmoid; and behind, by the body of the sphenoid, the sphenoidal concha, the ala of the vomer and the sphenoidal process of the palatine bone. In the cribriform plate of the ethmoid are the foramina for the olfactory nerves, and on the posterior part of the roof is the opening into the sphenoidal sinus. 9

FIG. 195– Medial wall of left nasal fossa. (See enlarged image)

The floor is flattened from before backward and concave from side to side. It is formed by the palatine process of the maxilla and the horizontal part of the palatine bone; near its anterior end is the opening of the incisive canal. 10

FIG. 196– Roof, floor, and lateral wall of left nasal cavity. (See enlarged image)

The medial wall (septum nasi) (Fig. 195), is frequently deflected to one or other side, more often to the left than to the right. It is formed, in front, by the crest of the nasal bones and frontal spine; in the middle, by the perpendicular plate of the ethmoid; behind, by the vomer and the rostrum of the sphenoid; below, by the crest of the maxillæ and palatine bones. It presents, in front, a large, triangular notch, which receives the cartilage of the septum; and behind, the free edge of the vomer. Its surface is marked by numerous furrows for vessels and nerves and by the grooves for the nasopalatine nerve, and is traversed by sutures connecting the bones of which it is formed. 11
The lateral wall (Fig. 196) is formed, in front, by the frontal process of the maxilla and by the lacrimal bone; in the middle, by the ethmoid, maxilla, and inferior nasal concha; behind, by the vertical plate of the palatine bone, and the medial pterygoid plate of the sphenoid. On this wall are three irregular anteroposterior passages, termed the superior, middle, and inferior meatuses of the nose. The superior meatus, the smallest of the three, occupies the middle third of the lateral wall. It lies between the superior and middle nasal conchæ; the sphenopalatine foramen opens into it behind, and the posterior ethmoidal cells in front. The sphenoidal sinus opens into a recess, the sphenoethmoidal recess, which is placed above and behind the superior concha. The middle meatus is situated between the middle and inferior conchæ, and extends from the anterior to the posterior end of the latter. The lateral wall of this meatus can be satisfactorily studied only after the removal of the middle concha. On it is a curved fissure, the hiatus semilunaris, limited below by the edge of the uncinate process of the ethmoid and above by an elevation named the bulla ethmoidalis; the middle ethmoidal cells are contained within this bulla and open on or near to it. Through the hiatus semilunaris the meatus communicates with a curved passage termed the infundibulum, which communicates in front with the anterior ethmoidal cells and in rather more than fifty per cent. of skulls is continued upward as the frontonasal duct into the frontal air-sinus; when this continuity fails, the frontonasal duct opens directly into the anterior part of the meatus. Below the bulla ethmoidalis and hidden by the uncinate process of the ethmoid is the opening of the maxillary sinus (ostium maxillare); an accessory opening is frequently present above the posterior part of the inferior nasal concha. The inferior meatus, the largest of the three, is the space between the inferior concha and the floor of the nasal cavity. It extends almost the entire length of the lateral wall of the nose, is broader in front than behind, and presents anteriorly the lower orifice of the nasolacrimal canal. 12
The Anterior Nasal Aperture (Fig. 181) is a heart-shaped or pyriform opening, whose long axis is vertical, and narrow end upward; in the recent state it is much contracted by the lateral and alar cartilages of the nose. It is bounded above by the inferior borders of the nasal bones; laterally by the thin, sharp margins which separate the anterior from the nasal surfaces of the maxillæ; and below by the same borders, where they curve medialward to join each other at the anterior nasal spine. 13
The choanæ are each bounded above by the under surface of the body of the sphenoid and ala of the vomer; below, by the posterior border of the horizontal part of the palatine bone; laterally, by the medial pterygoid plate; they are separated from each other by the posterior border of the vomer. 14

Differences in the Skull Due to AgeAt birth the skull is large in proportion to the other parts of the skeleton, but its facial portion is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half in the adult. The frontal and parietal eminences are prominent, and the greatest width of the skull is at the level of the latter; on the other hand, the glabella, superciliary arches, and mastoid processes are not developed. Ossification of the skull bones is not completed, and many of them, e. g., the occipital, temporals, sphenoid, frontal, and mandible, consist of more than one piece. Unossified membranous intervals, termed fontanelles, are seen at the angles of the parietal bones; these fontanelles are six in number: two, an anterior and a posterior, are situated in the middle line, and two, an antero-lateral and a postero-lateral, on either side. 15
The anterior or bregmatic fontanelle (Fig. 197) is the largest, and is placed at the junction of the sagittal, coronal, and frontal sutures; it is lozenge-shaped, and measures about 4 cm. in its antero-posterior and 2.5 cm. in its transverse diameter. The posterior fontanelle is triangular in form and is situated at the junction of the sagittal and lambdoidal sutures. The lateral fontanelles (Fig. 198) are small, irregular in shape, and correspond respectively with the sphenoidal and mastoid angles of the parietal bones. An additional fontanelle is sometimes seen in the sagittal suture at the region of the obelion. The fontanelles are usually closed by the growth and extension of the bones which surround them, but sometimes they are the sites of separate ossific centers which develop into sutural bones. The posterior and lateral fontanelles are obliterated within a month or two after birth, but the anterior is not completely closed until about the middle of the second year. 16

FIG. 197– Skull at birth, showing frontal and occipital fonticuli. (See enlarged image)

The smallness of the face at birth is mainly accounted for by the rudimentary condition of the maxillæ and mandible, the non-eruption of the teeth, and the small size of the maxillary air sinuses and nasal cavities. At birth the nasal cavities lie almost entirely between the orbits, and the lower border of the anterior nasal aperture is only a little below the level of the orbital floor. With the eruption of the deciduous teeth there is an enlargement of the face and jaws, and these changes are still more marked after the second dentition. 17
The skull grows rapidly from birth to the seventh year, by which time the foramen magnum and petrous parts of the temporals have reached their full size and the orbital cavities are only a little smaller than those of the adult. Growth is slow from the seventh year until the approach of puberty, when a second period of activity occurs: this results in an increase in all directions, but it is especially marked in the frontal and facial regions, where it is associated with the development of the air sinuses. 18
Obliteration of the sutures of the vault of the skull takes place as age advances. This process may commence between the ages of thirty and forty, and is first seen on the inner surface, and some ten years later on the outer surface of the skull. The dates given are, however, only approximate, as it is impossible to state with anything like accuracy the time at which the sutures are closed. Obliteration usually occurs first in the posterior part of the sagittal suture, next in the coronal, and then in the lambdoidal. 19
In old age the skull generally becomes thinner and lighter, but in a small proportion of cases it increases in thickness and weight, owing to an hypertrophy of the inner table. The most striking feature of the old skull is the diminution in the size of the maxillæ and mandible consequent on the loss of the teeth and the absorption of the alveolar processes. This is associated with a marked reduction in the vertical measurement of the face and with an alteration in the angles of the mandible. 20

FIG. 198– Skull at birth, showing sphenoidal and mastoid fonticuli. (See enlarged image)

Sexual Differences in the SkullUntil the age of puberty there is little difference between the skull of the female and that of the male. The skull of an adult female is, as a rule, lighter and smaller, and its cranial capacity about 10 per cent. less, than that of the male. Its walls are thinner and its muscular ridges less strongly marked; the glabella, superciliary arches, and mastoid processes are less prominent, and the corresponding air sinuses are small or rudimentary. The upper margin of the orbit is sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault somewhat flattened. The contour of the face is more rounded, the facial bones are smoother, and the maxillæ and mandible and their contained teeth smaller. From what has been said it will be seen that more of the infantile characteristics are retained in the skull of the adult female than in that of the adult male. A well-marked male or female skull can easily be recognized as such, but in some cases the respective characteristics are so indistinct that the determination of the sex may be difficult or impossible. 21

CraniologySkulls vary in size and shape, and the term craniology is applied to the study of these variations. The capacity of the cranial cavity constitutes a good index of the size of the brain which it contained, and is most conveniently arrived at by filling the cavity with shot and measuring the contents in a graduated vessel. Skulls may be classified according to their capacities as follows: 22
1. Microcephalic, with a capacity of less than 1350 c.cm.—e.g., those of native Australians and Andaman Islanders. 23
2. Mesocephalic, with a capacity of from 1350 c.cm. to 1450 c.cm.—e.g., those of African negroes and Chinese. 24
3. Megacephalic, with a capacity of over 1450 c.cm.—e.g., those of Europeans, Japanese, and Eskimos. 25
In comparing the shape of one skull with that of another it is necessary to adopt some definite position in which the skulls should be placed during the process of examination. They should be so placed that a line carried through the lower margin of the orbit and upper margin of the external acoustic meatus is in the horizontal plane. The normæ of one skull can then be compared with those of another, and the differences in contour and surface form noted. Further, it is necessary that the various linear measurements used to determine the shape of the skull should be made between definite and easily localized points on its surface. The principal points may be divided into two groups: (1) those in the median plane, and (2) those on either side of it. 26
The Points in the Median Plane are the: 27
Mental Point. The most prominent point of the chin. 28
Alveolar Point or Prosthion. The central point of the anterior margin of the upper alveolar arch. 29
Subnasal Point. The middle of the lower border of the anterior nasal aperture, at the base of the anterior nasal spine. 30
Nasion. The central point of the frontonasal suture. 31
Glabella. The point in the middle line at the level of the superciliary arches. 32
Ophryon. The point in the middle line of the forehead at the level where the temporal lines most nearly approach each other. 33
Bregma. The meeting point of the coronal and sagittal sutures. 34
Obelion. A point in the sagittal suture on a level with the parietal foramina. 35
Lambda. The point of junction of the sagittal and lambdoidal sutures. 36
Occipital Point. The point in the middle line of the occipital bone farthest from the glabella. 37
Inion. The external occipital protuberance. 38
Opisthion. The mid-point of the posterior margin of the foramen magnum. 39
Basion. The mid-point of the anterior margin of the foramen magnum. 40
The Points on Either Side of the Median Plane are the: 41
Gonion. The outer margin of the angle of the mandible. 42
Dacryon. The point of union of the antero-superior angle of the lacrimal with the frontal bone and the frontal process of the maxilla. 43
Stephanion. The point where the temporal line intersects the coronal suture. 44
Pterion. The point where the great wing of the sphenoid joins the sphenoidal angle of the parietal. 45
Auricular Point. The center of the orifice of the external acoustic meatus. 46
Asterion. The point of meeting of the lambdoidal, mastoöccipital, and mastoparietal sutures. 47
The horizontal circumference of the cranium is measured in a plane passing through the glabella (Turner) or the ophryon (Flower) in front, and the occipital point behind; it averages about 50 cm. in the female and 52.5 cm. in the male. 48
The occipitofrontal or longitudinal arc is measured from the nasion over the middle line of the vertex to the opisthion: while the basinasal length is the distance between the basion and the nasion. These two measurements, plus the antero-posterior diameter of the foramen magnum, represent the vertical circumference of the cranium. 49
The length is measured from the glabella to the occipital point, while the breadth or greatest transverse diameter is usually found near the external acoustic meatus. The proportion of breadth to length (breadth X 100)/length is termed the cephalic index or index of breadth. 50
The height is usually measured from the basion to the bregma, and the proportion of height to length (height X 100)/length constitutes the vertical or height index. 51
In studying the face the principal points to be noticed are the proportion of its length and breadth, the shape of the orbits and of the anterior nasal aperture, and the degree of projection of the jaws. 52
The length of the face may be measured from the ophryon or nasion to the chin, or, if the mandible be wanting, to the alveolar point; while its width is represented by the distance between the zygomatic arches. By comparing the length with the width of the face, skulls may be divided into two groups; dolichofacial or leptoprosope (long faced) and brachyfacial or chemoprosope (short faced). 53
The orbital index signifies the proportion which the orbital height bears to the orbital width, thus: orbital height X 100/orbital width
54
The nasal index expresses the proportion which the width of the anterior nasal aperture bears to the height of the nose, the latter being measured from the nasion to the lower margin of the nasal aperture, thus:nasal width X 100/nasal height
55
The degree of projection of the jaws is determined by the gnathic or alveolar index, which represents the proportion between the basialveolar and basinasal lengths, thus:basialveolar length X 100/basinasal length
56
The following table, modified from that given by Duckworth, 51 illustrates how these different indices may be utilized in the classification of skulls: 57
Index. Classification. Nomenclature. Examples.
1. Cephalic Below 75 Dolichocephalic Kaffirs and Native Australians.

Between 75 and 80 Mesaticephalic Europeans and Chinese.
Above 80 Brachycephalic Mongolians and Andamans.
2. Orbital Below 84 Microseme Tasmanians and Native Australians.

Between 84 and 89 Mesoseme Europeans.
Above 89 Megaseme Chinese and Polynesians.
3. Nasal Below 48 Leptorhine Europeans.

Between 48 and 53 Mesorhine Japanese and Chinese.
Above 53 Platyrhine Negroes and Native Australians.
4. Gnathic Below 98 Orthognathous Europeans.

Between 98 and 103 Mesognathous Chinese and Japanese.
Above 103 Prognathous Native Australians.

The chief function of the skull is to protect the brain, and therefore those portions of the skull which are most exposed to external violence are thicker than those which are shielded from injury by overlying muscles. Thus, the skull-cap is thick and dense, whereas the temporal squamæ being protected by the temporales muscles, and the inferior occipital fossæ, being shielded by the muscles at the back of the neck, are thin and fragile. Fracture of the skull is further prevented by its elasticity, its rounded shape, and its construction of a number of secondary elastic arches, each made up of a single bone. The manner in which vibrations are transmitted through the bones of the skull is also of importance as regards its protective mechanism, at all events as far as the base is concerned. In the vault, the bones being of a fairly equal thickness and density, vibrations are transmitted in a uniform manner in all directions, but in the base, owing to the varying thickness and density of the bones, this is not so; and therefore in this situation there are special buttresses which serve to carry the vibrations in certain definite directions. At the front of the skull, on either side, is the ridge which separates the anterior from the middle fossa of the base; and behind, the ridge or buttress which separates the middle from the posterior fossa; and if any violence is applied to the vault, the vibrations would be carried along these buttresses to the sella turcica, where they meet. This part has been termed the “center of resistance,” and here there is a special protective mechanism to guard the brain. The subarachnoid cavity at the base of the brain is dilated, and the cerebrospinal fluid which fills it acts as a water cushion to shield the brain from injury. In like manner, when violence is applied to the base of the skull, as in falls upon the feet, the vibrations are carried backward through the occipital crest, and forward through the basilar part of the occipital and body of the sphenoid to the vault of the skull. 58

FIG. 199– The premaxilla and its sutures. (After Albrecht.) (See enlarged image)

In connection with the bones of the face a common malformation is cleft palate. The cleft usually starts posteriorly, and its most elementary form is a bifid uvula; or the cleft may extend through the soft palate; or the posterior part of the whole of the hard palate may be involved, the cleft extending as far forward as the incisive foramen. In the severest forms, the cleft extends through the alveolus and passes between the incisive or premaxillary bone and the rest of the maxilla; that is to say, between the lateral incisor and canine teeth. In some instances, the cleft runs between the central and lateral incisor teeth; and this has induced some anatomists to believe that the premaxillary bone is developed from two centers (Fig. 199) and not from one, as was stated on p. 163. The medial segment, bearing a central incisor, is called an endognathion; the lateral segment, bearing the lateral incisor, is called a mesognathion. The cleft may affect one or both sides; if the latter, the central part is frequently displaced forward and remains united to the septum of the nose, the deficiency in the alveolus being complicated with a cleft in the lip (hare-lip). On examining a cleft palate in which the alveolus is not implicated, the cleft will generally appear to be in the median line, but occasionally is unilateral and in some cases bilateral. To understand this it must be borne in mind that three processes are concerned in the formation of the palate—the palatine processes of the two maxillæ, which grow in horizontally and unite in the middle line, and the ethmovomerine process, which grows downward from the base of the skull and frontonasal process to unite with the palatine processes in the middle line. In those cases where the palatine processes fail to unite with each other and with the medial process, the cleft of the palate is median; where one palatine process unites with the medial septum, the other failing to do so, the cleft in the palate is unilateral. In some cases where the palatine processes fail to meet in the middle, the ethmovomerine process grows downward between them and thus produces a bilateral cleft. Occasionally there may be a hole in the middle line of the hard palate, the anterior part of the hard and the soft palate being perfect; this is rare, because, as a rule, the union of the various processes progresses from before backward, and therefore the posterior part of the palate is more frequently defective than the anterior. 59
Note 50. See footnote, page 150. [back]
Note 51. Morphology and Anthropology, by W. L. H. Duckworth, M.A., Cambridge University Press. [back]

The bones by which the upper and lower limbs are attached to the trunk constitute respectively the shoulder and pelvic girdles. The shoulder girdle or girdle of the superior extremity is formed by the scapulæ and clavicles, and is imperfect in front and behind. In front, however, it is completed by the upper end of the sternum, with which the medial ends of the clavicles articulate. Behind, it is widely imperfect, the scapulæ being connected to the trunk by muscles only. The pelvic girdle or girdle of the inferior extremity is formed by the hip bones, which articulate with each other in front, at the symphysis pubis. It is imperfect behind, but the gap is filled in by the upper part of the sacrum. The pelvic girdle, with the sacrum, is a complete ring, massive and comparatively rigid, in marked contrast to the lightness and mobility of the shoulder girdle. 1

6a. The Bones of the Upper Extremity. 1. The Clavicle

(Ossa Extremitatis Superioris) & (Clavicula; Collar Bone)

The clavicle (Figs. 200, 201) forms the anterior portion of the shoulder girdle. It is a long bone, curved somewhat like the italic letter f, and placed nearly horizontally at the upper and anterior part of the thorax, immediately above the first rib. It articulates medially with the manubrium sterni, and laterally with the acromion of the scapula. 52 It presents a double curvature, the convexity being directed forward at the sternal end, and the concavity at the scapular end. Its lateral third is flattened from above downward, while its medial two-thirds is of a rounded or prismatic form. 1

Lateral Third.—The lateral third has two surfaces, an upper and a lower; and two borders, an anterior and a posterior. 2

Surface.—The upper surface is flat, rough, and marked by impressions for the attachments of the Deltoideus in front, and the Trapezius behind; between these impressions a small portion of the bone is subcutaneous. The under surface is flat. At its posterior border, near the point where the prismatic joins with the flattened portion, is a rough eminence, the coracoid tuberosity (conoid tubercle); this, in the natural position of the bone, surmounts the coracoid process of the scapula, and gives attachment to the conoid ligament. From this tuberosity an oblique ridge, the oblique or trapezoid ridge, runs forward and lateralward, and afford attachment to the trapezoid ligament. 3

Borders.—The anterior border is concave, thin, and rough, and gives attachment to the Deltoideus. The posterior border is convex, rough, thicker than the anterior, and gives attachment to the Trapezius. 4

Medial Two-thirds.—The medial two-thirds constitute the prismatic portion of the bone, which is curved so as to be convex in front, concave behind, and is marked by three borders, separating three surfaces. 5

FIG. 200– Left clavicle. Superior surface. (See enlarged image)

Borders.—The anterior border is continuous with the anterior margin of the flat portion. Its lateral part is smooth, and corresponds to the interval between the attachments of the Pectoralis major and Deltoideus; its medial part forms the lower boundary of an elliptical surface for the attachment of the clavicular portion of the Pectoralis major, and approaches the posterior border of the bone. The superior border is continuous with the posterior margin of the flat portion, and separates the anterior from the posterior surface. Smooth and rounded laterally, it becomes rough toward the medial third for the attachment of the Sternocleidomastoideus, and ends at the upper angle of the sternal extremity. The posterior or subclavian border separates the posterior from the inferior surface, and extends from the coracoid tuberosity to the costal tuberosity; it forms the posterior boundary of the groove for the Subclavius, and gives attachment to a layer of cervical fascia which envelops the Omohyoideus. 6

FIG. 201– Left clavicle. Inferior surface. (See enlarged image)

Surfaces.—The anterior surface is included between the superior and anterior borders. Its lateral part looks upward, and is continuous with the superior surface of the flattened portion; it is smooth, convex, and nearly subcutaneous, being covered only by the Platysma. Medially it is divided by a narrow subcutaneous area into two parts: a lower, elliptical in form, and directed forward, for the attachment of the Pectoralis major; and an upper for the attachment of the Sternocleidomastoideus. The posterior or cervical surface is smooth, and looks backward toward the root of the neck. It is limited, above, by the superior border; below, by the subclavian border; medially, by the margin of the sternal extremity; and laterally, by the coracoid tuberosity. It is concave medio-laterally, and is in relation, by its lower part, with the transverse scapular vessels. This surface, at the junction of the curves of the bone, is also in relation with the brachial plexus of nerves and the subclavian vessels. It gives attachment, near the sternal extremity, to part of the Sternohyoideus; and presents, near the middle, an oblique foramen directed lateralward, which transmits the chief nutrient artery of the bone. Sometimes there are two foramina on the posterior surface, or one on the posterior and another on the inferior surface. The inferior or subclavian surface is bounded, in front, by the anterior border; behind, by the subclavian border. It is narrowed medially, but gradually increases in width laterally, and is continuous with the under surface of the flat portion. On its medial part is a broad rough surface, the costal tuberosity (rhomboid impression), rather more than 2 cm. in length, for the attachment of the costoclavicular ligament. The rest of this surface is occupied by a groove, which gives attachment to the Subclavius; the coracoclavicular fascia, which splits to enclose the muscle, is attached to the margins of the groove. Not infrequently this groove is subdivided longitudinally by a line which gives attachment to the intermuscular septum of the Subclavius. 7

The Sternal Extremity (extremitas sternalis; internal extremity).—The sternal extremity of the clavicle is triangular in form, directed medialward, and a little downward and forward; it presents an articular facet, concave from before backward, convex from above downward, which articulates with the manubrium sterni through the intervention of an articular disk. The lower part of the facet is continued on to the inferior surface of the bone as a small semi-oval area for articulation with the cartilage of the first rib. The circumference of the articular surface is rough, for the attachment of numerous ligaments; the upper angle gives attachment to the articular disk. 8

The Acromial Extremity (extremitas acromialis; outer extremity).—The acromial extremity presents a small, flattened, oval surface directed obliquely downward, for articulation with the acromion of the scapula. The circumference of the articular facet is rough, especially above, for the attachment of the acromioclavicular ligaments. 9
In the female, the clavicle is generally shorter, thinner, less curved, and smoother than in the male. In those persons who perform considerable manual labor it becomes thicker and more curved, and its ridges for muscular attachment are prominently marked. 10

Structure.—The clavicle consists of cancellous tissue, enveloped by a compact layer, which is much thicker in the intermediate part than at the extremities of the bone. 11

Ossification.—The clavicle begins to ossify before any other bone in the body; it is ossified from three centers—viz., two primary centers, a medial and a lateral, for the body, 53 which appear during the fifth or sixth week of fetal life; and a secondary center for the sternal end, which appears about the eighteenth or twentieth year, and unites with the rest of the bone about the twenty-fifth year. 12
Note 52. The clavicle acts especially as a fulcrum to enable the muscles to give lateral motion to the arm. It is accordingly absent in those animals whose fore-limbs are used only for progression, but is present for the most part in animals whose anterior extremities are clawed and used for prehension, though in some of them—as, for instance, in a large number of the carnivora—it is merely a rudimentary bone suspended among the muscles, and not articulating with either the scapula or sternum. [back]
Note 53. Mall, American Journal of Anatomy, vol. v; Fawcett, Journal of Anatomy and Physiology, vol. xlvii. [back]

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