4b. The Parathyroid Glands

The parathyroid glands (Fig. 1177) are small brownish-red bodies, situated as a rule between the posterior borders of the lateral lobes of the thyroid gland and its capsule. They differ from it in structure, being composed of masses of cells arranged in a more or less columnar fashion with numerous intervening capillaries. They measure on an average about 6 mm. in length, and from 3 to 4 mm. in breadth, and usually present the appearance of flattened oval disks. They are divided, according to their situation, into superior and inferior. The superior, usually two in number, are the more constant in position, and are situated, one on either side, at the level of the lower border of the cricoid cartilage, behind the junction of the pharynx and esophagus. The inferior, also usually two in number, may be applied to the lower edge of the lateral lobes, or placed at some little distance below the thyroid gland, or found in relation to one of the inferior thyroid veins. 181 1

FIG. 1177– Parathyroid glands. (Halsted and Evans.) (See enlarged image)

In man, they number four as a rule; fewer than four were found in less than 1 per cent. of over a thousand persons (Pepere 182), but more than four in over 33 per cent. of 122 bodies examined by Civalleri. In addition, numerous minute islands of parathyroid tissue may be found scattered in the connective tissue and fat of the neck around the parathyroid glands proper, and quite distinct from them. 2

Development.—The parathyroid bodies are developed as outgrowths from the third and fourth branchial pouches (Figs. 1175). 3
A pair of diverticula arise from the fifth branchial pouch and form what are termed the ultimo-branchial bodies (Fig. 1175): these fuse with the thyroid gland, but probably contribute no true thyroid tissue. 4

Structure.—Microscopically the parathyroids consist of intercommunicating columns of cells supported by connective tissue containing a rich supply of blood capillaries. Most of the cells are clear, but some, larger in size, contain oxyphil granules. Vesicles containing colloid have been described as occurring in the parathyroid, but the observation has not been confirmed. 5
No doubt the parathyroid glands produce an internal secretion essential to the well-being of the human economy; but it is still a matter of dispute what symptoms of disease are produced by their removal and suppression of their secretion. Pepere believes that they show signs of exceptional activity during pregnancy, and that parathyroid insufficiency is a main factor in the production of tetany in infants and adults, of eclampsia, and of certain sorts of fits. It is probable that the tetany following parathyroidectomy is due to the accumulation of ammonium carbonate and Kendall has suggested that the function of the parathyroid is to convert ammonium carbonate into urea. 6
Note 181. Consult an article “Concerning the Parathyroid Glands,” by D. A. Welsh, Journal of Anatomy and Physiology, vol. xxxii. [back]
Note 182. Consult Le Ghiandole paratiroidee, by A. Pepere, Turin, 1906. [back]

4c. The Thymus

The thymus (Fig. 1178) is a temporary organ, attaining its largest size at the time of puberty (Hammar), when it ceases to grow, gradually dwindles, and almost disappears. If examined when its growth is most active, it will be found to consist of two lateral lobes placed in close contact along the middle line, situated partly in the thorax, partly in the neck, and extending from the fourth costal cartilage upward, as high as the lower border of the thyroid gland. It is covered by the sternum, and by the origins of the Sternohyoidei and Sternothyreoidei. Below, it rests upon the pericardium, being separated from the aortic arch and great vessels by a layer of fascia. In the neck it lies on the front and sides of the trachea, behind the Sternohyoidei and Sternothyreoidei. The two lobes generally differ in size; they are occasionally united, so as to form a single mass; and sometimes separated by an intermediate lobe. The thymus is of a pinkish-gray color, soft, and lobulated on its surfaces. It is about 5 cm. in length, 4 cm. in breadth below, and about 6 mm. in thickness. At birth it weighs about 15 grams, at puberty it weighs about 35 grams; after this it gradually decreases to 25 grams at twentyfive years, less than 15 grams at sixty, and about 6 grams at seventy years. 1

FIG. 1178– The thymus of a full-time fetus, exposed in situ. (See enlarged image)

Development.—The thymus appears in the form of two flask-shaped entodermal diverticula, which arise, one on either side, from the third branchial pouch (Fig. 1175), and extend lateralward and backward into the surrounding mesoderm in front of the ventral aortæ. Here they meet and become joined to one another by connective tissue, but there is never any fusion of the thymus tissue proper. The pharyngeal opening of each diverticulum is soon obliterated, but the neck of the flask persists for some time as a cellular cord. By further proliferation of the cells lining the flask, buds of cells are formed, which become surrounded and isolated by the invading mesoderm. In the latter, numerous lymphoid cells make their appearance, and are agregated to form lymphoid follicles. These lymphoid cells are probably derivatives of the entodermal cells which lined the original diverticula and their subdivisions. Additional portions of thymus tissue are sometimes developed from the fourth branchial pouches. Thymus continues to grow until the time of puberty and then begins to atrophy. 2

FIG. 1179– Minute structure of thymus. Follicle of injected thymus from calf, four days old, slightly diagrammatic, magnified about 50 diameters. The large vessels are disposed in two rings, one of which surrounds the follicle, the other lies just within the margin of the medulla. (Watney.) A and B. From thymus of camel, examined without addition of any reagent. Magnified about 400 diameters. A. Large colorless cell, containing small oval masses of hemoglobin. Similar cells are found in the lymph glands, spleen, and medulla of bone. B. Colored blood corpuscles. (See enlarged image)

Structure.—Each lateral lobe is composed of numerous lobules held together by delicate areolar tissue; the entire gland being enclosed in an investing capsule of a similar but denser structure. The primary lobules vary in size from that of a pin’s head to that of a small pea, and are made up of a number of small nodules or follicles, which are irregular in shape and are more or less fused together, especially toward the interior of the gland. Each follicle is from 1 to 2 mm. in diameter and consists of a medullary and a cortical portion, and these differ in many essential particulars from each other. The cortical portion is mainly composed of lymphoid cells, supported by a network of finely branched cells, which is continuous with a similar network in the medullary portion. This network forms an adventitia to the bloodvessels. In the medullary portion the reticulum is coarser than in the cortex, the lymphoid cells are relatively fewer in number, and there are found peculiar nest-like bodies, the concentric corpuscles of Hassall. These concentric corpuscles are composed of a central mass, consisting of one or more granular cells, and of a capsule which is formed of epithelioid cells (Fig. 1179). They are the remains of the epithelial tubes which grow out from the third branchial pouches of the embryo to form the thymus. 3
Each follicle is surrounded by a vascular plexus, from which vessels pass into the interior, and radiate from the periphery toward the center, forming a second zone just within the margin of the medullary portion. In the center of the medullary portion there are very few vessels, and they are of minute size. 4
Watney has made the important observation that hemoglobin is found in the thymus, either in cysts or in cells situated near to, or forming part of, the concentric corpuscles. This hemo globin occurs as granules or as circular masses exactly resembling colored blood corpuscles. He has also discovered, in the lymph issuing from the thymus, similar cells to those found in the gland, and, like them, containing hemoglobin in the form of either granules or masses. From these facts he arrives at the conclusion that the gland is one source of the colored blood corpuscles. More recently Schaffer has observed actual nucleated red-blood corpuscles in the thymus. The function of the thymus is obscure. It seems to furnish during the period of growth an internal secretion concerned with some phases of body metabolism, especially that of the sexual glands. 5

Vessels and Nerves.—The arteries supplying the thymus are derived from the internal mammary, and from the superior and inferior thyroids. The veins end in the left innominate vein, and in the thyroid veins. The lymphatics are described on page 698. The nerves are exceedingly minute; they are derived from the vagi and sympathetic. Branches from the descendens hypoglossi and phrenic reach the investing capsule, but do not penetrate into the substance of the gland. 6

4d. The Hypophysis Cerebri

The hypophysis (pituitary body) (Fig. 1180) is a small reddish-gray body, about 1 cm. in diameter, attached to the end of the infundibulum of the brain and resting in the hypophyseal fossa. 1

FIG. 1180– The hypophysis cerebri in position. Shown in sagittal section. (See enlarged image)

FIG. 1181– Median sagittal through the hypophysis of an adult monkey. Semidiagrammatic. (Herring.) (See enlarged image)

The hypophysis consists of an anterior and a posterior lobe, which differ from one another in their mode of development and in their structure (Fig. 1181). The anterior lobe is the larger and is somewhat kidney-shaped, the concavity being directed backward and embracing the posterior lobe. It consists of a pars anterior and a pars intermedia, separated from each other by a narrow cleft, the remnant of the pouch or diverticulum. The pars anterior is extremely vascular and consists of epithelial cells of varying size and shape, arranged in cord-like trabeculæ or alveoli and separated by large, thin-walled bloodvessels. The pars intermedia is a thin lamina closely applied to the body and neck of the posterior lobe and extending onto the neighboring parts of the brain; it contains few bloodvessels and consists of finely granular cells between which are small masses of colloid material. The pars intermedia in spite of the fact that it arises in common with the pars anterior from the ectoderm of the primitive buccal cavity is often considered as a part of the posterior lobe which arises from the floor of the third ventricle of the brain. Although of nervous origin the posterior lobe contains no nerve cells or fibers. It consists of neuroglia cells and fibers and is invaded by columns which grow into it from the pars intermedia; imbedded in it are large quantities of a colloid substance histologically similar to that found in the thyroid gland. In certain of the lower vertebrates, e.g., fishes, nervous structures are present, and the lobe is of large size. 2

FIG. 1182– Vertical sections of the heads of early embryos of the rabbit. Magnified. (From Mihalkovics.) A. From an embryo 5 mm. long. B. From an embryo 6 mm. long. C. Vertical section of the anterior end of the notochord and hypophysis, etc., from an embryo 16 mm. long. In A the buccopharyngeal membrane is still present. In B it is in the process of disappearing, and the stomodeum now communicates with the primitive pharynx. am. Amnion. c. Fore-brain. ch. Notochord. f. Anterior extremity of fore-gut, i. h. Heart. if. Infundibulum. m. Wall of brain cavity. mc. Mid-brain. mo. Hind-brain. p. Original position of hypophyseal diverticulum, py. ph. Pharynx. sp.e. Sphenoethmoidal. bc. Central. sp.o. Sphenoöccipital parts of basis cranii. tha. Thalamus. (See enlarged image)

From the pars intermedia a substance, no doubt an internal secretion, causes constriction of the bloodvessels with rise of arterial blood-pressure. This substance seems to have a stimulating effect on most of the smooth muscles, acting directly upon the muscle causing contraction. It also increases the secretion of the urine; of the mammary glands when in functional activity; and of the cerebrospinal fluid. Extracts of this lobe also influence the general metabolism of the carbohydrates by accelerating the process of glycogenolysis in the liver. 3
The pars anterior exercises a stimulating effect on the growth of the skeleton and probably on connective tissues in general. 4
Enlargement of the hypophysis and of the cavity of the sella turcica are found in the rare disease acromegaly, which is characterized by gradual enlargement of the face, hands, and feet, with headache and often a peculiar type of blindness. This blindness is due to the pressure of the enlarging hypophysis on the optic chiasma (Fig. 1180). 5

Development of the Hypophysis Cerebri.—This in the adult consists of a large anterior, consisting of the pars anterior and the pars intermedia, and a small posterior lobe: the former is derived from the ectoderm of the stomodeum, the latter from the floor of the fore-brain. About the fourth week there appears a pouchlike diverticulum of the ectodermal lining of the roof of the stomodeum. This diverticulum, pouch of Rathke (Fig. 1182), is the rudiment of the anterior lobe of the hypophysis; it extends upward in front of the cephalic end of the notochord and the remnant of the buccopharyngeal membrane, and comes into contact with the under surface of the fore-brain. It is then constricted off to form a closed vesicle, but remains for a time connected to the ectoderm of the stomodeum by a solid cord of cells. Masses of epithelial cells form on either side and in the front wall of the vesicle, and by the growth between these of a stroma from the mesoderm the development of the anterior lobe is completed. The upwardly directed hypophyseal involution becomes applied to the antero-lateral aspect of a downwardly directed diverticulum from the base of the fore-brain (page 744). This diverticulum constitutes the future infundibulum in the floor of the third ventricle while its inferior extremity becomes modified to form the posterior lobe of the hypophysis. In some of the lower animals the posterior lobe contains nerve cells and nerve fibers, but in man and the higher vertebrates these are replaced by connective tissue. A canal, craniopharyngeal canal, is sometimes found extending from the anterior part of the fossa hypophyseos of the sphenoid bone to the under surface of the skull, and marks the original position of Rathke’s pouch; while at the junction of the septum of the nose with the palate traces of the stomodeal end are occasionally present (Frazer). 6

4e. The Pineal Body

The pineal body (epiphysis) is a small reddish-gray body, about 8 mm. in length which lies in the depression between the superior colliculi. It is attached to the roof of the third ventricle near its junction with the mid-brain. It develops as an outgrowth from the third ventricle of the brain. 1
In early life it has a glandular structure which reaches its greatest development at about the seventh year. Later, especially after puberty, the glandular tissue gradually disappears and is replaced by connective tissue. 2

Structure.—The pineal body is destitute of nervous substance, and consists of follicles lined by epithelium and enveloped by connective tissue. These follicles contain a variable quantity of gritty material, composed of phosphate and carbonate of calcium, phosphate of magnesium and ammonia, and a little animal matter. 3
It contains a substance which if injected intravenously causes fall of blood-pressure. It seems probable that the gland furnishes an internal secretion in children that inhibits the development of the reproductive glands since the invasion of the gland in children, by pathological growths which practically destroy the glandular tissue, results in accelerated development of the sexual organs, increased growth of the skeleton and precocious mentality. 4

4f. The Chromaphil and Cortical Systems

Chromaphil or chromaffin cells, so-called because they stain yellow or brownish with chromium salts, are associated with the ganglia of the sympathetic nervous system. 1

Development.—They arise in common with the sympathetic cells from the neural crest, and are therefore ectodermal in origin. The chromaphil and sympathetic cells are indistinguishable from one another at the time of their migration from the spinal ganglia to the regions occupied in the adult. Differentiation of chromaphil cells begins in embryos about 18 mm. in length but is not complete until about birth. The chromaphiloblasts increase in size more than the sympathoblasts and stain less intensely with ordinary dyes. Later the chrome reaction develops. The aortic bodies differentiate first and are prominent in 20 mm. embryos. The paraganglia of the sympathetic plexuses differentiate next and last of all the paraganglia of the sympathetic trunk. The carotid body is completely differentiated in 30 mm. embryos. After birth the chromaphil organs degenerate but the paraganglia can be recognized with the microscope in sites originally occupied by them. 2
The paraganglia are small groups of chromaphil cells connected with the ganglia of the sympathetic trunk and the ganglia of the celiac, renal, suprarenal, aortic and hypogastric plexuses. They are sometimes found in connection with the ganglia of other sympathetic plexuses. None have been found with the sympathetic ganglia associated with the branches of the trigeminal nerve. 3
The aortic glands or bodies are the largest of these groups of chromaphil cells and measure in the newborn about 1 cm. in length. They lie one on either side of the aorta in the region of the inferior mesenteric artery. They decrease in size with age and after puberty are only visible with the microscope. About forty they disappear entirely. Other groups of chromaphil cells have been found associated with the sympathetic plexuses of the abdomen independently of the ganglia. 4
The medullary portions of the suprarenal glands and the glomus caroticum belong to the chromaphil system. 5

the Suprarenal Glands (Glandulæ Suprarenalis; Adrenal Capsule) (Figs. 1183, 1184)—The suprarenal glands are two small flattened bodies of a yellowish color, situated at the back part of the abdomen, behind the peritoneum, and immediately above and in front of the upper end of each kidney; hence their name. The right one is somewhat triangular in shape, bearing a resemblance to a cocked hat; the left is more semilunar, usually larger, and placed at a higher level than the right. They vary in size in different individuals, being sometimes so small as to be scarcely detected: their usual size is from 3 to 5 cm. in length, rather less in width, and from 4 to 6 mm. in thickness. Their average weight is from 1.5 to 2.5 gm. each. 6

Development.—Each suprarenal gland consists of a cortical portion derived from the celomic epithelium and a medullary portion originally composed of sympatho-chromaffin tissue. The cortical portion is first recognizable about the beginning of the fourth week as a series of buds from the celomic cells at the root of the mesentery. Later it becomes completely separated from the celomic epithelium and forms a suprarenal ridge projecting into the celom between the mesonephros and the root of the mesentery. Into this cortical portion cells from the neighboring masses of sympatho-chromaffin tissue migrate along the line of its central vein to reach and form the medullary portion of the gland. 7

Relations.—The relations of the suprarenal glands differ on the two sides of the body. 8
The right suprarenal is situated behind the inferior vena cava and right lobe of the liver, and in front of the diaphragm and upper end of the right kidney. It is roughly triangular in shape; its base, directed downward, is in contact with the medial and anterior aspects of the upper end of the right kidney. It presents two surfaces for examination, an anterior and a posterior. The anterior surface looks forward and lateralward, and has two areas: a medial, narrow, and non-peritoneal, which lies behind the inferior vena cava; and a lateral, somewhat triangular, in contact with the liver. The upper part of the latter surface is devoid of peritoneum, and is in relation with the bare area of the liver near its lower and medial angle, while its inferior portion is covered by peritoneum, reflected onto it from the inferior layer of the coronary ligament; occasionally the duodenum overlaps the inferior portion. A little below the apex, and near the anterior border of the gland, is a short furrow termed the hilum, from which the suprarenal vein emerges to join the inferior vena cava. The posterior surface is divided into upper and lower parts by a curved ridge: the upper, slightly convex, rests upon the diaphragm; the lower, concave, is in contact with the upper end and the adjacent part of the anterior surface of the kidney. 9
The left suprarenal, slightly larger than the right, is crescentic in shape, its concavity being adapted to the medial border of the upper part of the left kidney. It presents a medial border, which is convex, and a lateral, which is concave; its upper end is narrow, and its lower rounded. Its anterior surface has two areas: an upper one, covered by the peritoneum of the omental bursa, which separates it from the cardiac end of the stomach, and sometimes from the superior extremity of the spleen; and a lower one, which is in contact with the pancreas and lienal artery, and is therefore not covered by the peritoneum. On the anterior surface, near its lower end, is a furrow or hilum, directed downward and forward, from which the suprarenal vein emerges. Its posterior surface presents a vertical ridge, which divides it into two areas; the lateral area rests on the kidney, the medial and smaller on the left crus of the diaphragm. 10

FIG. 1183– Suprarenal glands viewed from the front. (See enlarged image)

FIG. 1184– Suprarenal glands viewed from behind. (See enlarged image)

The surface of the suprarenal gland is surrounded by areolar tissue containing much fat, and closely invested by a thin fibrous capsule, which is difficult to remove on account of the numerous fibrous processes and vessels entering the organ through the furrows on its anterior surface and base. 11
Small accessory suprarenals (glandulæ suprarenales accessoriæ) are often to be found in the connective tissue around the suprarenals. The smaller of these, on section, show a uniform surface, but in some of the larger a distinct medulla can be made out. 12

Structure.—On section, the suprarenal gland is seen to consist of two portions (Fig. 1185): an external or cortical and an internal or medullary. The former constitutes the chief part of the organ, and is of a deep yellow color; the medullary substance is soft, pulpy, and of a dark red or brown color. 13
The cortical portion (substantia corticalis) consists of a fine connective-tissue net-work, in which is imbedded the glandular epithelium. The epithelial cells are polyhedral in shape and possess rounded nuclei; many of the cells contain coarse granules, others lipoid globules. Owing to differences in the arrangement of the cells, three distinct zones can be made out: (1) the zona glomerulosa, situated beneath the capsule, consists of cells arranged in rounded groups, with here and there indications of an alveolar structure; the cells of this zone are very granular, and stain deeply. (2) The zona fasciculata, continuous with the zona glomerulosa, is composed of columns of cells arranged in a radial manner; these cells contain finer granules and in many instances globules of lipoid material. (3) The zona reticularis, in contact with the medulla, consists of cylindrical masses of cells irregularly arranged; these cells often contain pigment granules which give this zone a darker appearance than the rest of the cortex. 14
The medullary portion (substantia medullaris) is extremely vascular, and consists of large chromaphil cells arranged in a network. The irregular polyhedral cells have a finely granular cystoplasm that are probably concerned with the secretion of adrenalin. In the meshes of the cellular network are large anastomosing venous sinuses (sinusoids) which are in close relationship with the chromaphil or medullary cells. In many places the endothelial lining of the blood sinuses is in direct contact with the medullary cells. Some authors consider the endothelium absent in places and here the medullary cells are directly bathed by the blood. This intimate relationship between the chromaphil cells and the blood stream undoubtedly facilitates the discharge of the internal secretion into the blood. There is a loose meshwork of supporting connective tissue containing non-striped muscle fibers. This portion of the gland is richly supplied with non-medullated nerve fibers, and here and there sympathetic ganglia are found. 15

FIG. 1185– Section of a part of a suprarenal gland. (Magnified.) (See enlarged image)

Vessels and Nerves.—The arteries supplying the suprarenal glands are numerous and of comparatively large size; they are derived from the aorta, the inferior phrenic, and the renal. They subdivide into minute branches previous to entering the cortical part of the gland, where they break up into capillaries which end in the venous plexus of the medullary portion. 16
The suprarenal vein returns the blood from the medullary venous plexus and receives several branches from the cortical substance; it emerges from the hilum of the gland and on the right side opens into the inferior vena cava, on the left into the renal vein. 17
The lymphatics end in the lumbar glands. 18
The nerves are exceedingly numerous, and are derived from the celiac and renal plexuses, and, according to Bergmann, from the phrenic and vagus nerves. They enter the lower and medial part of the capsule, traverse the cortex, and end around the cells of the medulla. They have numerous small ganglia developed upon them in the medullary portion of the gland. 19
In connection with the development of the medulla from the sympathochromaffin tissue, it is to be noted that this portion of the gland secretes a substance, adrenalin, which has a powerful influence on those muscular tissues which are supplied by sympathetic fibers. 20

Glomus Caroticum (Carotid Glands; Carotid Bodies)—The carotid bodies, two in number, are situated one on either side of the neck, behind the common carotid artery at its point of bifurcation into the external and internal carotid trunks. They are reddish brown in color and oval in shape, the long diameter measuring about 5 mm. 21

FIG. 1186– Section of part of human glomus caroticum. (Schaper.) Highly magnified. Numerous bloodvessels are seen in section among the gland cells. (See enlarged image)

Each is invested by a fibrous capsule and consists largely of spherical or irregular masses of cells (Fig. 1186), the masses being more or less isolated from one another by septa which extend inward from the deep surface of the capsule. The cells are polyhedral in shape, and each contains a large nucleus imbedded in finely granular protoplasm, which is stained yellow by chromic salts. Numerous nerve fibers, derived from the sympathetic plexus on the carotid artery, are distributed throughout the organ, and a net-work of large sinusoidal capillaries ramifies among the cells. 22

FIG. 1187– Section of an irregular nodule of the glomus coccygeum. (Sertoli.) X 85. The section shows the fibrous covering of the nodule, the bloodvessels within it, and the epithelial cells of which it is constituted. (See enlarged image)

Glomus Coccygeum (Coccygeal Gland or Body; Luschka’s Gland)—The glomus coccygeum is placed in front of, or immediately below, the tip of the coccyx. It is about 2.5 mm. in diameter and is irregularly oval in shape; several smaller nodules are found around or near the main mass. 23
It consists of irregular masses of round or polyhedral cells (Fig. 1187), the cells of each mass being grouped around a dilated sinusoidal capillary vessel. Each cell contains a large round or oval nucleus, the protoplasm surrounding which is clear, and is not stained by chromic salts. 183 24
Note 183. Consult the following article: “Über die menschliche Steissdrüse,” von J. W. Thomson Walker, Archiv für mikroskopische Anatomie und Entwickelungsgeschichte, Band 64, 1904. [back]

4g. The Spleen

(Lien)

The spleen is situated principally in the left hypochondriac region, but its superior extremity extends into the epigastric region; it lies between the fundus of the stomach and the diaphragm. It is the largest of the ductless glands, and is of an oblong, flattened form, soft, of very friable consistence, highly vascular, and of a dark purplish color. 1

Development.—The spleen appears about the fifth week as a localized thickening of the mesoderm in the dorsal mesogastrium above the tail of the pancreas. With the change in position of the stomach the spleen is carried to the left, and comes to lie behind the stomach and in contact with the left kidney. The part of the dorsal mesogastrium which intervened between the spleen and the greater curvature of the stomach forms the gastrosplenic ligament. 2

Relations.—The diaphragmatic surface (facies diaphragmatica; external or phrenic surface) is convex, smooth, and is directed upward, backward, and to the left, except at its upper end, where it is directed slightly medialward. It is in relation with the under surface of the diaphragm, which separates it from the ninth, tenth, and eleventh ribs of the left side, and the intervening lower border of the left lung and pleura. 3

FIG. 1188– The visceral surface of the spleen. (See enlarged image)

The visceral surface (Fig. 1188) is divided by a ridge into an anterior or gastric and a posterior or renal portion. 4
The gastric surface (facies gastrica), which is directed forward, upward, and medialward, is broad and concave, and is in contact with the posterior wall of the stomach; and below this with the tail of the pancreas. It presents near its medial border a long fissure, termed the hilum. This is pierced by several irregular apertures, for the entrance and exit of vessels and nerves. 5
The renal surface (facies renalis) is directed medialward and downward. It is somewhat flattened, is considerably narrower than the gastric surface, and is in relation with the upper part of the anterior surface of the left kidney and occasionally with the left suprarenal gland. 6
The superior extremity (extremitas superior) is directed toward the vertebral column, where it lies on a level with the eleventh thoracic vertebra. The lower extremity or colic surface (extremitas inferior) is flat, triangular in shape, and rests upon the left flexure of the colon and the phrenicocolic ligament, and is generally in contact with the tail of the pancreas. The anterior border (margo anterior) is free, sharp, and thin, and is often notched, especially below; it separates the diaphragmatic from the gastric surface. The posterior border (margo posterior), more rounded and blunter than the anterior, separates the renal from the diaphragmatic surface; it corresponds to the lower border of the eleventh rib and lies between the diaphragm and left kidney. The intermediate margin is the ridge which separates the renal and gastric surfaces. The inferior border (internal border) separates the diaphragmatic from the colic surface. 7
The spleen is almost entirely surrounded by peritoneum, which is firmly adherent to its capsule. It is held in position by two folds of this membrane. One, the phrenicolienal ligament, is derived from the peritoneum, where the wall of the general peritoneal cavity comes into contact with the omental bursa between the left kidney and the spleen; the lienal vessels pass between its two layers (Fig. 1039). The other fold, the gastrolienal ligament, is also formed of two layers, derived from the general cavity and the omental respectively, where they meet between the spleen and stomach (Fig. 1039); the short gastric and left gastroepiploic branches of the lienal artery run between its two layers. The lower end of the spleen is supported by the phrenicocolic ligament (see page 1155). 8
The size and weight of the spleen are liable to very extreme variations at different periods of life, in different individuals, and in the same individual under different conditions. In the adult it is usually about 12 cm. in length, 7 cm. in breadth, and 3 or 4 cm. in thickness, and weighs about 200 grams. At birth its weight, in proportion to the entire body, is almost equal to what is observed in the adult, being as 1 to 350; while in the adult it varies from 1 to 320 and 400. In old age the organ not only diminishes in weight, but decreases considerably in proportion to the entire body, being as 1 to 700. The size of the spleen is increased during and after digestion, and varies according to the state of nutrition of the body, being large in highly fed, and small in starved animals. In malarial fever it becomes much enlarged, weighing occasionally as much as 9 kilos. 9
Frequently in the neighborhood of the spleen, and especially in the gastrolienal ligament and greater omentum, small nodules of splenic tissue may be found, either isolated or connected to the spleen by thin bands of splenic tissue. They are known as accessory spleens (lien accessorius; supernumerary spleen). They vary in size from that of a pea to that of a plum. 10

Structure.—The spleen is invested by two coats: an external serous and an internal fibroelastic coat. 11
The external or serous coat (tunica serosa) is derived from the peritoneum; it is thin, smooth, and in the human subject intimately adherent to the fibroelastic coat. It invests the entire organ, except at the hilum and along the lines of reflection of the phrenicolienal and gastrolienal ligaments. 12
The fibroelastic coat (tunica albuginea) invests the organ, and at the hilum is reflected inward upon the vessels in the form of sheaths. From these sheaths, as well as from the inner surface of the fibroelastic coat, numerous small fibrous bands, trabeculæ (Fig. 1189), are given off in all directions; these uniting, constitute the frame-work of the spleen. The spleen therefore consists of a number of small spaces or areolæ, formed by the trabeculæ; in these areolæ is contained the splenic pulp. 13
The fibroelastic coat, the sheaths of the vessels, and the trabeculæ, are composed of white and yellow elastic fibrous tissues, the latter predominating. It is owing to the presence of the elastic tissue that the spleen possesses a considerable amount of elasticity, which allows of the very great variations in size that it presents under certain circumstances. In addition to these constituents of this tunic, there is found in man a small amount of non-striped muscular fiber; and in some mammalia, e. g., dog, pig, and cat, a large amount, so that the trabeculæ appear to consist chiefly of muscular tissue. 14

FIG. 1189– Transverse section of the spleen, showing the trabecular tissue and the splenic vein and its tributaries. (See enlarged image)

FIG. 1190– Transverse section of the human spleen, showing the distribution of the splenic artery and its branches. (See enlarged image)

The splenic pulp (pulpa lienis) is a soft mass of a dark reddish-brown color, resembling grumous blood; it consists of a fine reticulum of fibers, continuous with those of the trabeculæ, to which are applied flat, branching cells. The meshes of the reticulum are filled with blood, in which, however, the white corpuscles are found to be in larger proportion than they are in ordinary blood. Large rounded cells, termed splenic cells, are also seen; these are capable of ameboid movement, and often contain pigment and red-blood corpuscles in their interior. The cells of the reticulum each possess a round or oval nucleus, and like the splenic cells, they may contain pigment granules in their cytoplasm; they do not stain deeply with carmine, and in this respect differ from the cells of the Malpighian bodies. In the young spleen, giant cells may also be found, each containing numerous nuclei or one compound nucleus. Nucleated red-blood corpuscles have also been found in the spleen of young animals. 15

Bloodvessels of the Spleen.—The lienal artery is remarkable for its large size in proportion to the size of the organ, and also for its tortuous course. It divides into six or more branches, which enter the hilum of the spleen and ramify throughout its substance (Fig. 1190), receiving sheaths from an involution of the external fibrous tissue. Similar sheaths also invest the nerves and veins. 16
Each branch runs in the transverse axis of the organ, from within outward, diminishing in size during its transit, and giving off in its passage smaller branches, some of which pass to the anterior, others to the posterior part. These ultimately leave the trabecular sheaths, and terminate in the proper substance of the spleen in small tufts or pencils of minute arterioles, which open into the interstices of the reticulum formed by the branched sustentacular cells. Each of the larger branches of the artery supplies chiefly that region of the organ in which the branch ramifies, having no anastomosis with the majority of the other branches. 17
The arterioles, supported by the minute trabeculæ, traverse the pulp in all directions in bundles (pencilli) of straight vessels. Their trabecular sheaths gradually undergo a transformation, become much thickened, and converted into adenoid tissue; the bundles of connective tissue becoming looser and their fibrils more delicate, and containing in their interstices an abundance of lymph corpuscles (W. Müller). 18

FIG. 1191– Transverse section of a portion of the spleen. (See enlarged image)

The altered coat of the arterioles, consisting of adenoid tissue, presents here and there thickenings of a spheroidal shape, the lymphatic nodules (Malpighian bodies of the spleen). These bodies vary in size from about 0.25 mm. to 1 mm. in diameter. They are merely local expansions or hyperplasiæ of the adenoid tissue, of which the external coat of the smaller arteries of the spleen is formed. They are most frequently found surrounding the arteriole, which thus seems to tunnel them, but occasionally they grow from one side of the vessel only, and present the appearance of a sessile bud growing from the arterial wall. In transverse sections, the artery, in the majority of cases, is found in an eccentric position. These bodies are visible to the naked eye on the surface of a fresh section of the organ, appearing as minute dots of a semiopaque whitish color in the dark substance of the pulp. In minute structure they resemble the adenoid tissue of lymph glands, consisting of a delicate reticulum, in the meshes of which lie ordinary lymphoid cells (Fig. 1191). The reticulum is made up of extremely fine fibrils, and is comparatively open in the center of the corpuscle, becoming closer at its periphery. The cells which it encloses are possessed of ameboid movement. When treated with carmine they become deeply stained, and can be easily distinguished from those of the pulp. 19
The arterioles end by opening freely into the splenic pulp; their walls become much attenuated, they lose their tubular character, and the endothelial cells become altered, presenting a branched appearance, and acquiring processes which are directly connected with the processes of the reticular cells of the pulp (Fig. 1192). In this manner the vessels end, and the blood flowing through them finds its way into the interstices of the reticulated tissue of the splenic pulp. Thus the blood passing through the spleen is brought into intimate relation with the elements of the pulp, and no doubt undergoes important changes. 20
After these changes have taken place the blood is collected from the interstices of the tissue by the rootlets of the veins, which begin much in the same way as the arteries end. The connective-tissue corpuscles of the pulp arrange themselves in rows, in such a way as to form an elongated space or sinus. They become elongated and spindle-shaped, and overlap each other at their extremities, and thus form a sort of endothelial lining of the path or sinus, which is the radicle of a vein. On the outer surfaces of these cells are seen delicate transverse lines or markings, which are due to minute elastic fibrillæ arranged in a circular manner around the sinus. Thus the channel obtains an external investment, and gradually becomes converted into a small vein, which after a short course acquires a coat of ordinary connective tissue, lined by a layer of flattened epithelial cells which are continuous with the supporting cells of the pulp. The smaller veins unite to form larger ones; these do not accompany the arteries, but soon enter the trabecular sheaths of the capsule, and by their junction form six or more branches, which emerge from the hilum, and, uniting, constitute the lienal vein, the largest radicle of the portal vein. 21

FIG. 1192– Section of the spleen, showing the termination of the small bloodvessels. (See enlarged image)

The veins are remarkable for their numerous anastomoses, while the arteries hardly anastomose at all. 22
The lymphatics are described on page 711. 23
The nerves are derived from the celiac plexus and are chiefly non-medullated. They are distributed to the bloodvessels and to the smooth muscle of the capsule and trabeculæ. 24

1. Surface Anatomy of the Head and Neck

Bones (Fig. 1193).—Various bony surfaces and prominences on the skull can be easily identified by palpation. The external occipital protuberance is situated behind, in the middle line, at the junction of the skin of the neck with that of the head. The superior nuchal line runs lateralward from it on either side, while extending downward from it is the median nuchal crest, situated deeply at the bottom of the nuchal furrow. Above the superior nuchal lines the vault of the cranium is thinly covered with soft structures, so that the form of this part of the head is almost that of the upper portion of the occipital, the parietal, and the frontal bones. The superior nuchal line can be followed lateralward to the mastoid portion of the temporal bone, from which the mastoid process projects downward and forward behind the ear. The anterior and posterior borders, the apex, and the external surface of this process are all available for superficial examination. The anterior border lies immediately behind the concha, and the apex is on a level with the lobule of the auricula. About 1 cm. below and in front of the apex of the mastoid process, the transverse process of the atlas can be distinguished. In front of the ear the zygomatic arch can be felt throughout its entire length; its posterior end is narrow and is situated a little above the level of the tragus; its anterior end is broad and is continued into the zygomatic bone. The lower border of the arch is more distinct than the upper, which is obscured by the attachment of the temporal fascia. In front, and behind, the upper border of the arch can be followed into the superior temporal line. In front, this line begins at the zygomatic process of the frontal bone as a curved ridge which runs at first forward and upward on the frontal bone, and then curving backward separates the forehead from the temporal fossa. It can then be traced across the parietal bone, where, though less marked, it can generally be recognized. Finally, it curves downward, and forward, and passing above the external acoustic meatus, ends in the posterior root of the zygomatic arch. Near the line of the greatest transverse diameter of the head are the parietal eminences, one on either side of the middle line; further forward, on the forehead, are the frontal eminences, which vary in prominence in different individuals and are frequently unsymmetrical. Below the frontal eminences the superciliary arches, which indicate the position of the frontal sinuses, can be recognized; as a rule they are small in the female and absent in children. In some cases the prominence of the superciliary arches is related to the size of the frontal sinuses, but frequently there is no such relationship. Situated between, and connecting the superciliary ridges, is a smooth, somewhat triangular area, the glabella, below which the nasion (frontonasal suture) can be felt as a slight depression at the root of the nose. 1

FIG. 1193– Side view of head, showing surface relations of bones. (See enlarged image)

Below the nasion the nasal bones, scantily covered by soft tissues, can be traced to their junction with the nasal cartilages, and on either side of the nasal bone the complete outline of the orbital margin can be made out. At the junction of the medial and intermediate thirds of the supraorbital margin the supraorbital notch, when present, can be felt; close to the medial end of the infraorbital margin is a little tubercle which serves as a guide to the position of the lacrimal sac. Below and lateral to the orbit, on either side, is the zygomatic bone forming the prominence of the cheek; its posterior margin is easily palpable, and on it just above the level of the lateral palpebral commissure is the zygomatic tubercle. A slight depression, about 1 cm. above this tubercle, indicates the position of the zygomaticofrontal suture. Directly below the orbit a considerable part of the anterior surface of the maxilla and the whole of its alveolar process can be palpated. The outline of the mandible can be recognized throughout practically its entire extent; in front of the tragus and below the zygomatic arch is the condyle, and from this the posterior border of the ramus can be followed to the angle; from the angle to the symphysis the lower rounded border of the mandible can be easily traced; the lower part of the anterior border of the ramus and the alveolar process can be made out without difficulty. In the receding angle below the chin is the hyoid bone, and the finger can be carried along the bone to the tip of the greater cornu, which is on a level with the angle of the mandible: the greater cornu is most readily appreciated by making pressure on one side, when the cornu of the opposite side will be rendered prominent and can be felt distinctly beneath the skin. 2

Joints and Muscles.—The temporomandibular articulation is quite superficial, and is situated below the posterior end of the zygomatic arch, in front of the external acoustic meatus. Its position can be ascertained by defining the condyle of the mandible; when the mouth opens, the condyle advances out of the mandibular fossa on to the articular tubercle, and a depression is felt in the situation of the joint. 3
The outlines of the muscles of the head and face cannot be traced on the surface except in the case of the Masseter and Temporalis. The muscles of the scalp are so thin that the outline of the bone is perceptible beneath them. Those of the face are small, covered by soft skin, and often by a considerable layer of fat, and their outlines are therefore concealed; they serve, however, to round off and smooth prominent borders, and to fill up what would otherwise be unsightly angular depressions. Thus the Orbicularis oculi rounds off the prominent margin of the orbit, and the Procerus fills in the sharp depression below the glabella. In like manner the labial muscles converging to the lips, and assisted by the superimposed fat, fill up the sunken hollow of the lower part of the face. When in action the facial muscles produce the various expressions, and in addition throw the skin into numerous folds and wrinkles. The Masseter imparts fulness to the hinder part of the cheek; if firmly contracted, as when the teeth are clenched, its quadrilateral outline is plainly visible; the anterior border forms a prominent vertical ridge, behind which is a considerable fulness especially marked at the lower part of the muscle. The Temporalis is fan-shaped and fills the temporal fossa, substituting for the concavity a somewhat convex swelling, the anterior part of which, on account of the absence of hair on the overlying skin, is more marked than the posterior, and stands out in strong relief when the muscle is in action. 4

FIG. 1194– Anterolateral view of head and neck. (See enlarged image)

In the neck, the Platysma when contracted throws the skin into oblique ridges parallel with the fasciculi of the muscle. The Sternocleidomastoideus has the most important influence on the surface form of the neck (Figs. 1194, 1195). When the muscle is at rest its anterior border forms an oblique rounded edge ending below in the sharp outline of the sternal head; the posterior border is only distinct for about 2 or 3 cm. above the middle of the clavicle. During contraction, the sternal head stands out as a sharply defined ridge, while the clavicular head is flatter and less prominent; between the two heads is a slight depression: the fleshy middle portion of the muscle appears as an oblique elevation with a thick, rounded, anterior border, best marked in its lower part. The sternal heads of the two muscles are separated by a V-shaped depression, in which are the Sternohyoideus and Sternothyreoideus. 5
Above the hyoid bone, near the middle line, the anterior belly of the Digastricus produces a slight convexity. 6
The anterior border of the Trapezius presents as a faint ridge running from the superior nuchal line, downward and forward to the junction of the intermediate and lateral thirds of the clavicle. Between the Sternocleidomastoideus and the Trapezius is the posterior triangle of the neck, the lower part of which appears as a shallow concavity—the supraclavicular fossa. In this fossa, the inferior belly of the Omohyoideus, when in action, presents as a rounded cord-like elevation a little above, and almost parallel to, the clavicle. 7

FIG. 1195– Front view of neck. (See enlarged image)

Arteries.—The positions of several of the larger arteries can be ascertained from their pulsations. 8
The subclavian artery can be felt by making pressure downward, backward, and medialward behind the clavicular head of the Sternocleidomastoideus; its transverse cervical branch may be detected parallel to, and about a finger’s breadth above, the clavicle. The common and external carotid arteries can be recognized immediately beneath the anterior edge of the Sternocleidomastoideus. The external maxillary artery can be traced over the border of the mandible just in front of the anterior border of the Masseter, then about 1 cm. lateral to the angle of the mouth, and finally as it runs up the side of the nose. The pulsation of the occipital artery can be distinguished about 3 or 4 cm. lateral to the external occipital protuberance; that of the posterior auricular in the groove between the mastoid process and the auricula. The course of the superficial temporal artery can be readily followed across the posterior end of the zygomatic arch to a point about 3 to 5 cm. above this, where it divides into its frontal and parietal branches; the pulsation of the frontal branch is frequently visible on the side of the forehead. The supraorbital artery can usually be detected immediately above the supraorbital notch or foramen. 9

2. Surface Markings of Special Regions of the Head and Neck

The Cranium.—Scalp.—The soft parts covering the upper surface of the skull form the scalp and comprise the following layers (Fig. 1196): (1) skin, (2) subcutaneous tissue, (3) Occipitalis frontalis and galea aponeurotica, (4) subaponeurotic tissue, (5) pericranium. The subcutaneous tissue consists of a close mesh-work of fibers, the meshes of which contain fatty tissue; the fibers bind the skin and galea aponeurotica firmly together, so that when the Occipitalis or the Frontalis is in action the skin moves with the aponeurosis. The subaponeurotic tissue, which intervenes between the galea aponeurotica and the pericranium, is much looser in texture, and permits the movement of the aponeurosis over the underlying bones. 1

FIG. 1196– Diagrammatic section of scalp. (See enlarged image)

Bony Landmarks (Fig. 1193).—In addition to the bony points already described which can be determined by palpation, the following are utilized for surface markings: 2
Auricular Point.—The center of the orifice of the external acoustic meatus. 3
Preauricular Point.—A point on the posterior root of the zygomatic arch immediately in front of the external acoustic meatus. 4
Asterion.—The point of meeting of the lambdoidal, mastoöccipital, and mastoparietal sutures; it lies 4 cm. behind and 12 mm. above the level of the auricular point. 5
Pterion.—The point where the great wing of the sphenoid joins the sphenoidal angle of the parietal; it is situated 35 mm. behind, and 12 mm. above, the level of the frontozygomatic suture. 6
Inion.—The external occipital protuberance. 7
Lambda.—The point of meeting of the lambdoidal and sagittal sutures; it is in the middle line about 6.5 cm. above the inion. 8
Bregma.—The meeting-point of the coronal and sagittal sutures; it lies at the point of intersection of the middle line of the scalp with a line drawn vertically upward through the preauricular point. 9
A line passing through the inferior margin of the orbit and the auricular point is known as Reid’s base line. The lambdoidal suture can be indicated on either side by the upper two-thirds of a line from the lambda to the tip of the mastoid process. The sagittal suture is in the line joining the lambda to the bregma. The position of the coronal suture on either side is sufficiently represented by a line joining the bregma to the center of the zygomtic arch. 10
The floor of the middle fossa of the skull is at the level of the posterior three-fourths of the upper border of the zygomatic arch; the articular eminence of the temporal bone is opposite the foramen spinosum and the semilunar ganglion. 11

FIG. 1197– Drawing of a cast by Cunningham to illustrate the relations of the brain to the skull. (See enlarged image)

Brain (Figs. 1197, 1198).—The general outline of the cerebral hemisphere, on either side, may be mapped out on the surface in the following manner. Starting from the nasion, a line drawn along the middle of the scalp to the inion represents the superior border. The line of the lower margin behind is that of the transverse sinus (see page 1294), or more roughly a line convex upward from the inion to the posterior root of the zygomatic process of the temporal bone; thence along the posterior two-thirds of the upper border of the zygomatic arch where the line turns up to the pterion; the front part of the lower margin extends from the pterion to the glabella about 1 cm. above the supraorbital margin. The cerebellum is so deeply situated that there is no reliable surface marking for it; a point 4 cm. behind and 1.5 cm. below the level of the auricular point is situated directly over it. 12
The relations of the principal fissures and gyri of the cerebral hemispheres to the surface of the scalp are of considerable practical importance, and several methods of indicating them have been devised. Necessarily these methods can only be regarded as approximately correct, yet they are all sufficiently accurate for surgical purposes. The longitudinal fissure corresponds to the medial line of the scalp between the nasion and inion. In order to mark out the lateral cerebral (Sylvian) fissure a point, termed the Sylvian point, which practically corresponds to the pterion, is defined 35 mm. behind and 12 mm. above the level of the frontozygomatic suture; this point marks the spot where the lateral fissure divides. Another method of defining the Sylvian point is to divide the distance between the nasion and inion into four equal parts; from the junction of the third and fourth parts (reckoning from the front) draw a line to the frontozygomatic suture; from the junction of the first and second parts a line to the auricular point. These two lines intersect at the Sylvian point and the portion of the first line behind this point overlies the posterior ramus of the lateral cerebral fissure. The position of the posterior ramus can otherwise be obtained by joining the Sylvian point to a point 2 cm. below the summit of the parietal eminence. The anterior ascending ramus can be marked out by drawing a line upward at right angles to the line of the posterior ramus for 2 cm. and the anterior horizontal ramus by a line of the same length drawn horizontally forward—both from the Sylvian point. To define the central sulcus (fissure of Rolando) two points are taken; one is situated 1.25 cm. behind the center of the line joining the nasion and inion; the second is at the intersection of the line of the posterior ramus of the lateral cerebral fissure with a line through the preauricular point at right angles to Reid’s base line. The upper 9 cm. of the line joining these two points overlies the central sulcus and forms an angle, opening forward, of about 70° with the middle line of the scalp. An alternative method is to draw two perpendicular lines from Reid’s base line to the top of the head; one from the preauricular point and the other from the posterior border of the mastoid process at its root. A line from the upper end of the posterior line to the point where the anterior intersects the line of the posterior ramus of the lateral fissure indicates the position of the central sulcus. The precetral and postcentral sulci are practically parallel to the central sulcus; they are situated respectively about 15 mm. in front of, and behind, it. The superior frontal sulcus can be mapped out by a line drawn from the junction of the upper and middle thirds of the precentral sulcus, in a direction parallel with the longitudinal sulcus, to a point midway between the middle line of the forehead and the temporal line, 4 cm. above the supraorbital notch. The inferior frontal sulcus begins at the junction of the middle and lower thirds of the precentral sulcus, and follows the course of the superior temporal line. 13

FIG. 1198– Relations of the brain and middle meningeal artery to the surface of the skull. 1. Nasion. 2. Inion. 3. Lambda. 4. Lateral cerebral fissure. 5. Central sulcus. AA. Reid’s base line. B. Point for trephining the anterior branch of the middle meningeal artery. C. Suprameatal triangle. D. Sigmoid bend of the transverse sinus. E. Point for trephining over the straight portion of the transverse sinus, exposing dura mater of both cerebrum and cerebellum. Outline of cerebral hemisphere indicated in blue; course of middle meningeal artery in red. (See enlarged image)

The horizontal limb of the intraparietal sulcus begins from the junction of the lower with the middle third of the postcentral sulcus and curves backward parallel to the longitudinal fissure, midway between it and the parietal eminence; it then curves downward to end midway between the lambda and the parietal eminence. The external part of the parietoöccipital fissure runs lateralward at right angles to the longitudinal fissure for about 2.5 cm. from a point 5 mm. in front of the lambda. If the line of the posterior ramus of the lateral cerebral fissure be continued back to the longitudinal fissure, the last 2.5 cm. of it will indicate the position of the parietoöccipital fissure. 14
The lateral ventricle may be circumscribed by a quadrilateral figure. The upper limit is a horizontal line 5 cm. above the zygomatic arch; this defines the roof of the ventricle. The lower limit is a horizontal line 1 cm. above the zygomatic arch; it indicates the level of the end of the inferior horn. Two vertical lines, one through the junction of the anterior and middle thirds of the zygomatic arch, and the other 5 cm. behind the tip of the mastoid process, indicate the extent of the anterior horn in front and the posterior horn behind. 15

Vessels.—The line of the anterior division of the middle meningeal artery is equidistant from the frontozygomatic suture and the zygomatic arch; it is obtained by joining up the following points: (1) 2.5 cm., (2) 4 cm., and (3) 5 cm. from these two landmarks. The posterior division can be reached 2.5 cm. above the auricular point. 16
The position of the transverse sinus is obtained by taking two lines: the first from the inion to a point 2.5 cm. behind the auricular point; the second from the anterior end of the first to the tip of the mastoid process. The second line corresponds roughly to the line of reflection of the skin of the auricula behind, and its upper two-thirds represents the sigmoid part of the sinus. The first part of the sinus has a slight upward convexity, and its highest point is about 4 cm. behind and 1 cm. above the level of the auricular point. The width of the sinus is about 1 cm. 17

The Face.—Air Sinuses (Fig. 1199).—The frontal and maxillary sinuses vary so greatly in form and size that their surface markings must be regarded as only roughly approximate. To mark out the position of the frontal sinus three points are taken: (1) the nasion, (2) a point in the middle line 3 cm. above the nasion, (3) a point at the junction of the lateral and intermediate thirds of the supraorbital margin. By joining these a triangular field is described which overlies the greater part of the sinus. The outline of the maxillary sinus is irregularly quadrilateral and is obtained by joining up the following points: (1) the lacrimal tubercle, (2) a point on the zygomatic bone at the level of the inferior and lateral margins of the orbit, (3) and (4) points on the alveolar process above the last molar and the second premolar teeth respectively. 18

External Maxillary Artery.—The course of this artery on the face may be indicated by a line starting from the lower border of the mandible at the anterior margin of the Masseter, and running at first forward and upward to a point 1 cm. lateral to the angle of the mouth, thence to the ala of the nose and upward to the medial commissure of the eye (Fig. 1200). 19

Trigeminal Nerve.—Terminal branches of this nerve, viz., the supraorbital branch of the ophthalmic, the infraorbital of the maxillary, and the mental of the mandibular emerge from corresponding foramina on the face (Fig. 1200). The supraorbital foramen is situated at the junction of the medial and intermediate thirds of the supraorbital margin. A line drawn from this foramen to the lower border of the mandible, through the interval between the two lower premolar teeth, passes over the infraorbital and mental foramina; the former lies about 1 cm. below the margin of the orbit, while the latter varies in position according to the age of the individual; in the adult it is midway between the upper and lower borders of the mandible, in the child it is nearer the lower border, while in the edentulous jaw of old age it is close to the upper margin. 20

FIG. 1199– Outline of bones of face, showing position of air sinuses. (See enlarged image)

FIG. 1200– Outline of side of face, showing chief surface markings. (See enlarged image)

The position of the sphenopalatine ganglion is indicated from the side by a point on the upper border of the zygomatic arch, 6 mm. from the margin of the zygomatic bone. 21

Parotid Gland (Fig. 1200).—The upper border of the parotid gland corresponds to the posterior two-thirds of the lower border of the zygomatic arch; the posterior border to the front of the external acoustic meatus, the mastoid process, and the anterior border of Sternocleidomastoideus. The inferior border is indicated by a line from the tip of the mastoid process to the junction of the body and greater cornu of the hyoid bone. In front, the anterior border extends for a variable distance on the superficial surface of the Masseter. The surface marking for the parotid duct is a line drawn across the face about a finger’s breadth below the zygomatic arch, i. e., from the lower margin of the concha to midway between the red margin of the lip and the ala of the nose; the duct ends opposite the second upper molar tooth and measures about 5 cm. in length. 22

The Nose.—The outlines of the nasal bones and the cartilages forming the external nose can be easily felt. The mobile portion of the nasal septum, formed by the medial crura of the greater alar cartilages and the skin, is easily distinguished between the nares. When the head is tilted back and a speculum introduced through the naris, the floor of the nasal cavity, the lower part of the nasal septum, and the anterior ends of the middle and inferior nasal conchæ can be examined. The opening of the nasolacrimal duct, which lies under cover of the front of the inferior nasal concha, is situated about 2.5 cm. behind the naris and 2 cm. above the level of the floor of the nasal cavity. 23

FIG. 1201– The mouth cavity. The cheeks have been slit transversely and the tongue pulled forward. (See enlarged image)

The Mouth.—The orifice of the mouth is bounded by the lips, which are covered externally by the whitish skin and internally by the red mucous membrane. The size of the orifice varies considerably in different individuals, but seems to bear a close relationship to the size and prominence of the teeth; its angles usually correspond to the lateral borders of the canine teeth. Running down the center of the outer surface of the upper lip is a shallow groove—the philtrum. If the lips be everted there can be seen, in the middle line of each, a small fold of mucous membrane—the frenulum—passing from the lip to the gum. By pulling the angle of the mouth outward the mucous membrane of the cheek can be inspected, and on this, opposite the second molar tooth of the maxilla, is the little papilla which marks the orifice of the parotid duct. 24
In the floor of the mouth is the tongue (Fig. 1201). Its upper surface is convex and is marked along the middle line by a shallow sulcus; the anterior two-thirds are rough and studded with papillæ; the posterior third is smooth and tuberculated. The division between the anterior two-thirds and the posterior third is marked by a V-shaped furrow, the sulcus terminalis, which is situated immediately behind the line of the vallate papillæ. 25

FIG. 1202– The mouth cavity. The apex of the tongue is turned upward, and on the right side a superficial dissection of its under surface has been made. (See enlarged image)

On the under surface of the tongue (Fig. 1202) the mucous membrane is smooth and devoid of papillæ. In the middle line, the mucous membrane extends to the floor of the mouth as a distinct fold—the frenulum—the free edge of which runs forward to the symphysis menti. Sometimes the ranine vein can be seen immediately beneath the mucous membrane, a little lateral to the frenulum. Close to the attachment of the frenulum to the floor of the mouth, the slit-like orifice of the submaxillary duct is visible on either side. Running backward and lateralward from the orifice of the submaxillary duct is the plica sublingualis, produced by the projection of the sublingual gland which lies immediately beneath the mucous membrane. The plica serves also to indicate the line of the submaxillary duct and of the lingual nerve. At the back of the mouth is the isthmus faucium, bounded above by the palatine velum, from the free margin of which the uvula projects downward in the middle line. On either side of the isthmus are the two palatine arches, the anterior formed by the Glossopalatinus and the posterior by the Pharyngopalatinus. Between the two arches of either side is the palatine tonsil, above which is the small supratonsillar recess; the position of the tonsil corresponds to the angle of the mandible. When the mouth is opened widely, a tense band—the pterygomandibular raphé—can be seen and felt lateral to the glossopalatine arch. Its lower end is attached to the mandible behind the last molar tooth, and immediately below and in front of this the lingual nerve can be felt; the upper end of the ligament can be traced to the pterygoid hamulus. About 1 cm. in front of the hamulus and 1 cm. medial to the last molar tooth of the maxilla is the greater palatine foramen through which the descending palatine vessels and the anterior palatine nerve emerge. Behind the last molar tooth of the maxilla the coronoid process of the mandible is palpable. 26

FIG. 1203– Front of nasal part of pharynx, as seen with the laryngoscope. (See enlarged image)

FIG. 1204– Laryngoscopic view of interior of larynx (See enlarged image)

By tilting the head well back a portion of the posterior pharyngeal wall, corresponding to the site of the second and third cervical vertebræ, can be seen through the isthmus faucium. On introducing the finger the anterior surfaces of the upper cervical vertebræ can be felt through the thin muscular wall of the pharynx; if the finger be hooked round the palatine velum, the choanæ can be distinguished in front, and the pharyngeal ostium of the auditory tube on either side. The level of the choanæ is that of the atlas, while the palatine velum is opposite the body of the axis. 27
With the laryngoscope many other structures can be seen. In the nasal part of the pharynx (Fig. 1203), the choanæ, the nasal septum, the nasal conchæ, and the pharyngeal ostia of the auditory tubes can all be examined. Further down, the base of the tongue, the anterior surface of the epiglottis with the glossoepiglottic and pharyngoepiglottic folds bounding the valleculæ, and the piriform sinuses, are readily distinguished. Beyond these is the entrance to the larynx, bounded on either side by the aryepiglottic folds, in each of which are two rounded eminences corresponding to the corniculate and cuneiform cartilages. 28
Within the larynx (Fig. 1204) on either side are the ventricular and vocal folds (false and true vocal cords) with the ventricle between them. Still deeper are seen the cricoid cartilage and the anterior parts of some of the cartilaginous rings of the trachea, and sometimes, during deep inspiration, the bifurcation of the trachea. 29

The Eye.—The palpebral fissure is elliptical in shape, and varies in form in different individuals and in different races of mankind; normally it is oblique, in a direction upward and lateralward, so that the lateral commissure is on a slightly higher level than the medial. When the eyes are directed forward as in ordinary vision the upper part of the cornea is covered by the upper eyelid and its lower margin corresponds to the level of the free margin of the lower eyelid, so that usually the lower three-fourths are exposed. 30
At the medial commissure (Fig. 1205) are the caruncula lacrimalis and the plica semilunaris. When the lids are everted, the tarsal glands appear as a series of nearly straight parallel rows of light yellow granules. On the margins of the lids about 5 mm. from the medial commissure are two small openings—the lacrimal puncta; in the natural condition they are in contact with the conjunctiva of the bulb of the eye, so that it is necessary to evert the eyelids to expose them. The position of the lacrimal sac is indicated by a little tubercle which can be plainly felt on the lower margin of the orbit; the sac lies immediately above and medial to the tubercle. If the eyelids be drawn lateralward so as to tighten the skin at the medial commissure a prominent core can be felt beneath the tightened skin; this is the medial palpebral ligament, which lies over the junction of the upper with the lower two-thirds of the sac, thus forming a useful guide to its situation. The direction of the nasolacrimal duct is indicated by a line from the lacrimal sac to the first molar tooth of the maxilla; the length of the duct is about 12 or 13 mm. 31

FIG. 1205– Front of left eye with eyelids separated to show medial canthus. (See enlarged image)

On looking into the eye, the iris with its opening, the pupil, and the front of the lens can be examined, but for investigation of the retina an ophthalmoscope is necessary. With this the lens, the vessels of the retina, the optic disk, and the macula lutea can all be inspected (Fig. 1206). 32
On the lateral surface of the nasal part of the frontal bone the pulley of the Obliquus superior can be easily reached by pushing the finger backward along the roof of the orbit; the tendon of the muscle can be traced for a short distance backward and lateralward from the pulley. 33

FIG. 1206– The interior of the posterior half of the left eyeball. (See enlarged image)

The Ear.—The various prominences and fossæ of the auricula (see page 1034) are visible (Fig. 1207). The opening of the external acoustic meatus is exposed by drawing the tragus forward; at the orifice are a few short crisp hairs which serve to prevent the entrance of dust or of small insects; beyond this the secretion of the ceruminous glands serves to catch any small particles which may find their way into the meatus. The interior of the meatus can be examined through a speculum. At the line of junction of its bony and cartilaginous portions an obtuse angle is formed which projects into the antero-inferior wall and produces a narrowing of the lumen in this situation. The cartilaginous part, however, is connected to the bony part by fibrous tissue which renders the outer part of the meatus very movable, and therefore by drawing the auricula upward, backward, and slightly outward, the canal is rendered almost straight. In children the meatus is very short, and this should be remembered in introducing the speculum. 34

FIG. 1207– The auricula or pinna. Lateral surface. (See enlarged image)

Through the speculum the greater part of the tympanic membrane (Fig. 1208) is visible. It is a pearlygray membrane slightly glistening in the adult, placed obliquely so as to form with the floor of the meatus an angle of about 55°. At birth it is more horizontal and situated in almost the same plane as the base of the skull. The membrane is concave outward, and the point of deepest concavity—the umbo—is slightly below the center. Running upward and slightly forward from the umbo is a reddish-yellow streak produced by the manubrium of the malleus. This streak ends above just below the roof of the meatus at a small white rounded prominence which is caused by the lateral process of the malleus projecting against the membrane. The anterior and posterior malleolar folds extend from the prominence to the circumference of the membrane and enclose the pars flaccida. Behind the streak caused by the manubrium of the malleus a second streak, shorter and very faint, can be distinguished; this is the long crus of the incus. A narrow triangular patch extending downward and forward from the umbo reflects the light more brightly than any other part, and is usually described as the cone of light. 35

FIG. 1208– The right tympanic membrane as seen through a speculum. (See enlarged image)

FIG. 1209– Left temporal bone showing surface markings for the tympanic antrum (red), transverse sinus (blue), and facial nerve (yellow). (See enlarged image)

Tympanic Antrum.—The site of the tympanic antrum is indicated by the suprameatal triangle (Fig. 1209). This triangle is bounded above by the posterior root of the zygomatic arch; behind by a vertical line from the posterior border of the external acoustic meatus; in front and below by the upper margin of the meatus. 36

The Neck (Fig. 1210).—Larynx and Trachea.—In the receding angle below the chin, the hyoid bone (page 1288), situated opposite the fourth cervical vertebra, can easily be made out. A finger’s breadth below it is the laryngeal prominence of the thyroid cartilage; the space intervening between the hyoid bone and the thyroid cartilage is occupied by the hyothyroid membrane. The outlines of the thyroid cartilage are readily palpated; below its lower border is a depression corresponding to the middle cricothyroid ligament. The level of the vocal folds corresponds to the middle of the anterior margin of the thyroid cartilage. The anterior part of the cricoid cartilage forms an important landmark on the front of the neck; it lies opposite the sixth cervical vertebra, and indicates the junctions of pharynx with esophagus, and larynx with trachea. Below the cricoid cartilage the trachea can be felt, though it is only in thin subjects that the separate rings can be distinguished; as a rule there are seven or eight rings above the jugular notch of the sternum, and of these the second, third, and fourth are covered by the isthmus of the thyroid gland. 37

FIG. 1210– Side of neck, showing chief surface markings. (See enlarged image)

Muscles.—The posterior belly of Digastricus is marked out by a line from the tip of the mastoid process to the junction of the greater cornu and body of the hyoid bone; a line from this latter point to a point just lateral to the symphysis menti indicates the position of the anterior belly. The line of Omohyoideus begins at the lower border of the hyoid bone, curves downward and lateralward to cross Sternocleidomastoideus at the junction of its middle and lower thirds, i. e., opposite the cricoid cartilage, and then runs more horizontally to the acromial end of the clavicle. 38

Arteries.—The position of the common carotid artery in the neck is indicated by a line drawn from the upper part of the sternal end of the clavicle to a point midway between the tip of the mastoid process and the angle of the mandible. From the clavicle to the upper border of the thyroid cartilage this line overlies the common carotid artery, beyond this it is over the external carotid. The external carotid artery may otherwise be marked out by the upper part of a line from the side of the cricoid cartilage to the front of the external acoustic meatus, arching the line slightly forward. 39
The points of origin of the main branches of the external carotid in the neck are all related to the tip of the greater cornu of the hyoid bone as follows: (1) the superior thyroid, immediately below it; (2) the lingual, on a level with it; (3) the facial, and (4) the occipital a little above and behind it. 40
The subclavian artery is indicated on the surface by a curved line, convex upward, from the sternoclavicular articulation to the middle of the clavicle. The highest point of the convexity is from 1 to 3 cm. above the clavicle. 41

Veins.—The surface marking for the internal jugular vein is slightly lateral and parallel to that for the common carotid artery. The position of the external jugular vein is marked out by a line from the angle of the mandible to the middle of the clavicle. A point on this line about 4 cm. above the clavicle indicates the spot where the vein pierces the deep fascia. The line of the anterior jugular vein begins close to the symphysis menti, runs downward parallel with and a little to one side of the middle line and, at a variable distance above the jugular notch, turns lateralward to the external jugular. 42

Nerves.—The facial nerve at its exit from the stylomastoid foramen is situated about 2.5 cm. from the surface, opposite the middle of the anterior border of the mastoid process; a horizontal line from this point to the ramus of the mandible overlies the stem of the nerve. To mark the site of the accessory nerve a line is drawn from the angle of the mandible to a point on the anterior border of Sternocleidomastoideus about 3 to 4 cm. below the apex of the mastoid process, or to the midpoint of the posterior border of the muscle; the line is continued across the posterior triangle to Trapezius. 43
The cutaneous branches of the cervical plexus as they emerge from the posterior border of Sternocleidomastoideus may be indicated as follows: the lesser occipital begins immediately above the midpoint of the border and runs along the border to the scalp; the great auricular and cervical cutaneous both start from the middle of the border, the former running upward toward the lobule of the auricula, the latter crossing Sternocleidomastoideus at right angles to its long axis; the supraclavicular nerves emerge from immediately below the middle of the posterior border and run down over the clavicle. The phrenic nerve begins at the level of the middle of the thyroid cartilage and runs behind the clavicle about midway between the anterior and posterior borders of Sternocleidomastoideus. 44
The upper border of the brachial plexus is indicated by a line from the side of the cricoid cartilage to the middle of the clavicle. 45

Submaxillary Gland.—On either side of the neck the superficial portion of the submaxillary gland, as it lies partly under cover of the mandible, can be palpated. 46

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3. Surface Anatomy of the Back

Bones.—The only subcutaneous parts of the vertebral column are the apices of the spinous processes. These are distinguishable at the bottom of a furrow which runs down the middle line of the back from the external occipital protuberance to the middle of the sacrum. In the cervical region the furrow is broad and ends below in a conspicuous projection caused by the spinous processes of the seventh cervical and first thoracic vertebræ. Above this, the spinous process of the sixth cervical vertebra sometimes forms a projection; the other cervical spinous processes are sunken, but that of the axis can be felt. In the thoracic region the furrow is shallow and during stooping disappears, and then the spinous processes become more or less visible; the markings produced by them are small and close together. In the lumbar region the furrow is deep and the situations of the spinous processes are frequently indicated by little pits or depressions, especially when the muscles in the loins are well-developed. In the sacral region the furrow is shallower, presenting a flattened area which ends below at the most prominent part of the dorsal surface of the sacrum, i. e., the spinous process of the third sacral vertebra. At the bottom of the sacral furrow the irregular dorsal surface of the bone may be felt, and below this, in the deep groove running to the anus, the coccyx. 1
The only other portions of the vertebral column which can be felt from the surface are the transverse processes of the first, sixth, and seventh cervical vertebræ. 2

Muscles.—The muscles proper of the back are so obscured by those of the upper extremity (Fig. 1211) that they have very little influence on surface form. The Splenii by their divergence serve to broaden out the upper part of the back of the neck and produce a fulness in this situation. In the loin the Sacrospinales, bound down by the lumbodorsal fascia, form rounded vertical eminences which determine the depth of the spinal furrow and taper below to a point on the dorsal surface the sacrum. The continuations of the Sacrospinales in the lower thoracic region form flattened planes which are gradually lost on passing upward. 3

FIG. 1211– Surface anatomy of the back. (See enlarged image)

Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

4. Surface Markings of the Back

Bony Landmarks.—In order to identify any particular spinous process it is customary to count from the prominence caused by the seventh cervical and first thoracic; of these the latter is the more prominent. The root of the spine of the scapula is on a level with the tip of the spinous process of the third thoracic vertebra, and the inferior angle with that of the seventh. The highest point of the iliac crest is on a level with the spinous process of the fourth lumbar, and the posterior superior iliac spine with that of the second sacral. 1

FIG. 1212– Diagram showing the relation of the medulla spinalis to the dorsal surface of the trunk. The bones are outlined in red. (See enlarged image)

Level of body of No. of nerve. Level of tip of spine of Level of body of No. of nerve. Level of tip of spine of

C.1 C.1
T.8 T.9 7 T.
2 2
9 10 8

3 1 C. 10 11 9
3 4 2
12 10
4 5 3 11 L. 1 11
5 6 4
2

6 7 5 12 3

8 6
4 12
7 T. 1 7
5

T. 1 2 1 T.
S. 1

2 3
L. 1 2

3 4 2
3

4 5 3
4 1 L.
5 6 4
5

6 7 5
C. 1

7 8 6 L. 2

The transverse process of the atlas is about 1 cm. below and in front of the apex of the mastoid process. The transverse process of the sixth cervical vertebra is opposite the cricoid cartilage; below it is the transverse process of the seventh and occasionally a cervical rib. 2

FIG. 1213– Sagittal section of vertebral canal to show the lower end of the medulla spinalis and the flum terminale. (Testut.) Li, Lv. First and fifth lumbar vertebra. S?? Second sacral vertebra. 1. Dura mater. 2. Lower part of subarachnoid cavity. 3. Lower extremity of medulla spinalis. 4. Filum terminale internum, and 5. Filum terminale externum. 6. Attachment of filum terminale to first segment of cooccyx. (See enlarged image)

FIG. 1214– Scheme showing the relations of the regions of attachment of the spinal nerves to the vertebral spinous processes. (After Reid.) (See enlarged image)

Medulla Spinalis.—The position of the lower end of the medulla spinalis varies slightly with the movements of the vertebral column, but, in the adult, in the upright posture it is usually at the level of the spinous process of the second lumbar vertebra (Fig. 1212); at birth it lies at the level of the fourth lumbar. 3
The subdural and subarachnoid cavities end below opposite the spinous process of the third sacral vertebra (Fig. 1213). 4

Spinal Nerves (Fig. 1214).—The table on page 1305, after Macalister, shows the relations which the places of attachment of the nerves to the medulla spinalis present to the bodies and spinous processes of the vertebræ. 5