A text-book of veterinary anatomy

The radial artery is smaller than the ulnar. It descends on the flexor carpi internus, passes over the postero-internal surface of the carpus, and is continued as the internal deep volar metacarpal. At the distal end of the forearm and at the carpus it furnishes branches to the retia carpi. Another branch (A. met. perforans proximalis) runs outward between the suspensory ligament and the large metacarpal bone, passes through the proximal foramen of the bone, and unites with the interosseous artery; before passing through the foramen it detaches the middle deep volar metacarpal artery (A. met. volaris prof. III.), which descends on the posterior face of the metacarpal bone, receives an anastomotic branch from the internal deep artery, and concurs in the formation of the deep volar arch above the fetlock.

The ulnar artery, the larger of the two divisions of the median, descends under cover of the flexor carpi internus without giving off any large branches in the forearm. It passes through the carpal canal and continues along the inner side of the deep flexor tendon as the volar common digital artery. At the distal third of the metacarpus this vessel is joined by a branch from the internal deep volar metacarpal artery, forming the superficial volar arch. Near this another branch of the common digital (or of the internal digital) passes around the outer border of the flexor tendons to the posterior face of the metacarpal bone and concurs with the deep volar metacarpal arteries in the formation of the deep volar arch. A branch from the arch passes forward through the inferior foramen of the metacarpal bone and joins the dorsal metacarpal artery which descends from the rete carpi dorsale in the anterior metacarpal groove.

The volar common digital artery (A. metacarpea volaris superficialis III.) passes into the interdigital space and divides into two volar proper digital arteries, which descend along the interdigital surfaces of the chief digits and pass through the foramina at the upper part of the interdigital surfaces of the third phalanges, enter the cavities in these bones, and ramify in a manner similar to the corresponding vessels in the horse. The volar common digital detaches a branch (A. interdigitalis perforans) which passes forward through the upper part of the interdigital space and anastomoses with the dorsal metacarpal artery.

The volar proper digital arteries (or the common digital) give off, in addition to other collaterals, branches which correspond to the arteries of the plantar cushion of the horse. These pass to the bulbs of the claws and anastomose with each other and with the inner and outer digital arteries, forming an arch from which numerous branches are distributed to the matrix of the hoofs.

The dorsal metacarpal artery (A. met. dorsalis III.) is a small vessel which arises from the rete carpi dorsale, descends in the groove on the anterior face of the metacarpal bone, and is joined by the inferior perforating metacarpal artery from the deep volar arch to constitute the dorsal common digital artery. This vessel (A. digitalis communis dorsalis III.) divides into two dorsal proper digital arteries.

The internal digital artery (A. digiti III. medialis) is the continuation of the internal deep volar metacarpal artery. It descends on the inner side of the inner digit and terminates at the bulb of the claw by anastomosing with the corresponding volar proper digital artery. It gives off a branch to the rudimentary digit and forms a transverse anastomosis behind the first phalanx with the volar common digital or its inner division.

The external digital artery (A. digiti IV. lateralis) arises from the deep volar arch, passes down on the outer side of the external digit and is distributed like the inner one.

BRANCHES OF THE THORACIC AORTA

The bronchial and œsophageal arteries often arise separately.

Ten pairs of intercostal arteries usually arise from the aorta. The other three come from the subcostal artery.

The two phrenic arteries are very variable in origin. They may come from the aorta, the cœliac, left ruminal, or an intercostal or lumbar artery.

BRANCHES OF THE ABDOMINAL AORTA

The cœliac artery is about four to five inches (ca. 10 to 12 cm.) in length. It passes downward and curves forward between the rumen and pancreas on the left and the right crus of the diaphragm and the posterior vena cava on the right. It gives off five chief branches.

1. The hepatic artery arises from the convex side of the curve of the cœliac artery as it crosses the posterior vena cava. It passes downward, forward, and to the right above the portal vein to the portal fissure, and gives off the following branches:

(1) Pancreatic branches.

(2) Dorsal and ventral branches to the liver. The ventral branch is the larger; it gives off the right gastric artery, which runs in the lesser omentum to supply the origin of the duodenum and the pylorus, anastomosing with the dorsal branch of the omaso-abomasal artery.

(3) The cystic artery supplies the gall-bladder.

(4) The gastro-duodenal artery divides into right gastro-epiploic and pancreatico-duodenal branches. The right gastro-epiploic artery anastomoses with the left gastro-epiploic. The pancreatico-duodenal artery anastomoses with the first intestinal branch of the anterior mesenteric artery.

2. The right ruminal artery (A. ruminalis dextra) is the largest branch, and usually arises by a short common trunk with the splenic. It runs downward and backward on the right face of the dorsal sac of the rumen to the posterior transverse fissure, in which it turns around to the left and anastomoses with branches of the left ruminal artery. It gives off a pancreatic branch, dorsal and ventral coronary arteries, branches to the great omentum, and ramifies on both surfaces of the rumen.

3. The left ruminal artery (A. ruminalis sinistra) runs downward on the anterior part of the right face of the rumen, enters the anterior furrow, in which it runs from right to left, and continues backward in the left longitudinal groove, anastomosing with branches of the right artery. It supplies chiefly the left face of the rumen, but not its posterior part. It usually gives off near its origin the reticular artery (A. reticularis); this rather small vessel passes forward on the dorsal curvature of the rumen and turns downward in the rumino-reticular groove, in the bottom of which it runs around ventrally to the right side. It gives off a branch which passes to the left of the cardia and along the lesser curvature of the reticulum to the neck of the omasum. The reticular branches anastomose with the omaso-abomasal and left ruminal arteries.

4. The omaso-abomasal artery (A. gastrica sinistra) appears as the continuation of the cœliac. It passes forward and downward to the greater curvature of the omasum and divides after a course of four or five inches into two branches. The dorsal branch curves sharply backward on the dorsal surface of the omasum, continues along the lesser curvature of the abomasum, and anastomoses with the hepatic artery. It supplies branches to the omasum and to the lesser curvature and pyloric part of the abomasum. The ventral branch (A. gastroepiploica sinistra) runs forward and downward over the anterior extremity of the omasum, passes backward in the great omentum close to the ventral curvature of the abomasum, and anastomoses with the right gastro-epiploic. A considerable branch from it curves around in front of the neck of the omasum to communicate with the reticular artery. Another branch runs back across the left side of the omaso-abomasal junction, and a third goes to the lesser (ventral) curvature of the omasum.

5. The splenic artery usually arises by a common trunk with the right ruminal artery. It passes forward and to the left across the dorsal curvature of the rumen and enters the hilus of the spleen.

The anterior mesenteric artery arises from the aorta just behind the cœliac, and has about the same caliber as the latter. It passes downward and a little to the right, and crosses the colon as it emerges from the spiral to run backward. After detaching twigs to the pancreas it gives off in succession the following branches:

1. A branch (A. colica media) passes to the colon as it emerges from the spiral arrangement. This artery is comparable to the middle colic or artery of the small colon of the horse; it runs backward along the terminal part of the colon, which it supplies.

2. The ileo-cæco-colic artery ramifies on the right face of the spiral part of the colon. It gives off the ileo-cæcal artery, which divides into ileal and cæcal arteries.

3. An artery (Ramus collateralis) runs in the mesentery in a curve along the ventral border of the coils of the colon. (This vessel is absent in the sheep.)

4. An artery which constitutes the direct continuation of the anterior mesenteric pursues a course in the mesentery corresponding to the series of mesenteric lymph glands.

The two preceding vessels are essentially the arteries of the small intestine, which they supply with the exception of its initial and terminal parts. The first gives off no considerable branches in its course along the ventral border of the coils of the colon, but on curving upward along the latter it anastomoses with the second artery and detaches numerous branches to the small intestine which form series of superposed anastomotic arches. It supplies, roughly speaking, about one-third of the small intestine and terminates by joining the ileal artery. The second artery gives off numerous branches which also form arches and supply about the first two-thirds of the small intestine, exclusive of the small part supplied by branches of the cœliac artery. Both arteries give branches to the lymph glands.^[181]

The posterior mesenteric artery arises from the aorta near its termination. It is small and supplies branches to the terminal part of the colon and to the rectum.

The renal arteries arise from the aorta close together. The right one passes outward and forward across the dorsal face of the posterior vena cava to the hilus of the kidney. The left one runs backward, but necessarily varies in direction in conformity with the position of the kidney (q. v.).

The spermatic arteries resemble those of the horse.

The utero-ovarian arteries are small.

The five pairs of lumbar arteries derived from the aorta are distributed much as in the horse. The sixth usually comes from the internal iliac artery.

The middle sacral artery is a vessel about 5 mm. in diameter which continues the aorta. It arises from the dorsal face of the aorta at the angle of divergence of the internal iliacs, runs backward on the pelvic surface of the sacrum a little to the left of the median line, and is continued as the middle coccygeal artery. It gives off small collateral branches to the spinal cord and the muscles of the tail and the lateral coccygeal arteries. The latter may have a common trunk of origin, and each divides into dorsal and ventral branches. The middle coccygeal artery runs through the ventral (hæmal) arches of the coccygeal vertebræ. The coccygeal arteries are connected at pretty regular intervals by segmental anastomoses.

The internal iliac arteries are much longer than in the horse. Each passes backward on the sacro-sciatic ligament and divides about the middle of the pelvic wall into posterior gluteal and internal pudic branches. The chief differences in its distribution are: (1) A large trunk gives origin to the umbilical and middle uterine arteries. The umbilical artery is usually largely obliterated and its terminal branches receive their blood through anastomoses with the internal pudic. It gives off near its origin two small vessels, the ureteral artery (A. ureterica) and the deferential artery (A. deferentialis), which accompany the ureter and the vas deferens respectively. The middle uterine artery (A. uterina media) is very large. It is distributed chiefly to the cornu of the uterus, and compensates for the small size of the utero-ovarian artery. (2) The ilio-lumbar artery is relatively small and is distributed chiefly to the sublumbar muscles. It is sometimes replaced by branches of the circumflex iliac and gluteal arteries. (3) The anterior gluteal artery is commonly represented by several vessels. (4) The obturator artery is represented by several small branches which supply the obturator and adductor muscles. (5) The iliaco-femoral and lateral sacral arteries are absent. The absence of the latter is compensated by the middle sacral and gluteal arteries. (6) The posterior gluteal (or ischiatic) artery is large. It emerges through the lesser sciatic notch and ramifies in the biceps femoris and adjacent muscles. (7) The internal pudic artery (A. urethro-genitalis) is the direct continuation of the internal iliac. It gives off branches to the rectum, bladder, urethra, and genital organs. In the male it supplies the accessory genital glands and divides into dorsal and deep arteries of the penis; the a. dorsalis penis runs along the dorsum penis to the glans and gives twigs to the prepuce; the a. profunda penis gives off a perineal branch and enters the corpus cavernosum penis. In the female it gives off a large posterior uterine artery, which supplies the posterior part of the uterus and gives branches to the vagina and bladder. It ends as the a. clitoridis, which supplies the clitoris and adjacent parts.

ARTERIES OF THE PELVIC LIMB

The external iliac artery has the same course as in the horse. The circumflex iliac artery is large. A branch from it emerges between the abdominal and lumbar muscles near the external angle of the ilium and ramifies like the terminals of the ilio-lumbar artery of the horse.

The femoral and popliteal arteries pursue a similar course to those of the horse. The chief differences in their branches are as follows:

1. The external pudic artery is distributed chiefly to the scrotum in the male. In the cow it is usually termed the mammary and is very large, especially during lactation. Each divides at the base of the mammary gland into two branches which are distributed to the anterior and posterior parts (“quarters”) of the gland. A small branch accompanies the subcutaneous abdominal vein to the xiphoid region.

2. The deep femoral artery gives off an obturator branch which passes up through the obturator foramen to supply the obturator internus and compensates otherwise for the absence of the obturator artery.

3. The anterior femoral artery is large. It often gives off the external circumflex artery of the thigh, which perforates the proximal end of the quadriceps, gives branches to that muscle, the iliacus, glutei, and tensor fasciæ latæ.

4. The saphenous artery is large. It descends in front of the homonymous vein to the postero-internal surface of the hock, where it divides into two plantar branches. The internal plantar artery (A. plantaris medialis) is the direct continuation of the saphenous. It descends at first along the inner border of the superficial flexor tendon and is continued as the internal superficial plantar metatarsal artery along the inner side of the deep flexor tendon with the internal plantar nerve. It anastomoses at the proximal end of the metatarsus with the perforating metatarsal artery, assisting in the formation of the proximal plantar arch. Near the fetlock it concurs with the perforating branch of the dorsal metatarsal artery in the formation of the distal plantar arch. Below this it is continued as the internal digital artery. The external plantar artery (A. plantaris lateralis) is small. It descends along the outer border of the deep flexor tendon with the external plantar nerve, concurs with the perforating tarsal and the internal plantar arteries in the formation of the proximal plantar arch, and gives branches to the rete tarsi dorsale. Continuing downward along the deep flexor tendon as the external superficial plantar metatarsal artery, it assists in forming the distal plantar arch and becomes the external digital artery.

The posterior tibial artery is relatively small and is distributed chiefly to the muscles on the posterior surface of the tibia. Lower down it is replaced by the saphenous artery as described above.

The anterior tibial artery has the same course as in the horse. It is continued down the groove on the front of the metatarsal bone as the dorsal metatarsal artery. This is the chief artery of the region and is accompanied by two veins. It detaches the proximal perforating metatarsal artery, which passes through the proximal foramen of the metatarsal bone and concurs with the superficial plantar arteries in forming the proximal plantar arch. Near the distal end of the metatarsal bone it gives off the distal perforating metatarsal artery which passes back through the distal metatarsal foramen and assists in forming the distal plantar arch. The two arches are connected by the small deep plantar metatarsal artery which lies in the groove on the posterior face of the large metatarsal bone.

The dorsal common digital artery is the direct continuation of the dorsal metatarsal. It divides into two branches which unite in the interdigital space with the corresponding branches of the plantar common digital to form the proper digital arteries.

The plantar common digital artery descends from the distal plantar arch, anastomoses in the interdigital space with the internal and external digitals, and divides into two branches which join those of the dorsal common digital artery as before mentioned.

The foregoing is a brief statement of the more common arrangement of the vessels in the distal part of the limb, but minor variations are very common.

The Veins^[182]

The vena hemiazygos usually takes the place of the vena azygos. It lies along the left side of the aorta and the bodies of the thoracic vertebræ, turns down across the left face of the aorta and left pulmonary artery, runs back over the left auricle and opens into the great coronary vein or the right atrium. It receives the intercostal veins.

Two jugular veins occur on either side. The internal jugular vein (V. jugularis interna) is a relatively small vessel which accompanies the carotid artery. It arises by occipital, laryngeal, and thyroid radicles, receives tracheal, œsophageal, and muscular branches, and joins the external jugular near its termination. It is sometimes absent, but in some cases it appears, on the other hand, to be large enough to interfere with venesection practised on the external jugular. The external jugular vein (V. jugularis externa) is very large and corresponds to the single jugular of the horse. It is separated from the carotid artery in the greater part of its course by the sterno-cephalicus and omo-hyoideus muscles.

The inferior cerebral vein usually does not unite with the occipital; the latter is continued by the internal jugular vein.

The orbital veins form a network between the periorbita and the muscles of the eyeball. This plexus communicates with the cavernous sinus and with the superior cerebral vein. It is also drained by the frontal vein which runs in the supraorbital canal and groove and joins the angular vein of the eye.

The dorsal nasal vein is usually double.

The superior labial vein usually joins the infraorbital.

The vena reflexa is absent and the radicles which are received by it in the horse go to the internal maxillary vein.

The sublingual vein is very large.

The veins of the thoracic limb differ chiefly in the distal part; the special features are as follows:

The dorsal digital veins ascend on the front of the digits and are connected with the other digital veins by transverse branches. They unite near the fetlock to form the dorsal metacarpal vein. This runs upward on the anterior face of the metacarpus and carpus, inclines to the inner surface of the radius, and joins the accessory cephalic or the cephalic vein.

The volar digital veins are larger than the dorsal. They lie on the interdigital surfaces of the digits and unite in the interdigital space to form a trunk which is a satellite of the volar common digital artery.

The internal and external digital veins lie in front of the corresponding arteries. They are connected with the volar digital vein by a large branch which passes between the flexor tendons and the first phalanx. At the distal end of the metacarpus each inclines forward and anastomoses with the volar common digital vein to form the volar venous arch. The inner vein is continued as the internal volar metacarpal vein along the inner border of the suspensory ligament, and becomes a satellite of the radial artery in the forearm, while the outer one is continued on the posterior face of the metacarpal bone by two irregular veins, the external and middle volar metacarpals. The latter anastomose freely with each other and with the inner vein. They unite below the carpus or join the volar common digital vein.

The accessory cephalic vein is the upward continuation of the dorsal metacarpal vein and is much larger than in the horse.

The posterior vena cava is partially embedded in the medial border of the liver. Its abdominal part has a thicker wall than in the horse. Its affluents correspond to the arteries of which they are satellites. The renal veins are large and thick-walled; they run obliquely forward and join the vena cava at an acute angle. The left one is much the longer.

Two middle sacral veins usually accompany the artery.

The veins of the mammary glands deserve special notice. They converge to a venous circle at the base of the udder, which is drained chiefly by two pairs of veins. The subcutaneous abdominal vein (anterior mammary or “milk” vein) is very large in animals of the dairy breeds and its course along the ventral wall of the abdomen is easily followed. It is usually flexuous. It emerges at the anterior border of the udder about two or three inches (ca. 5 to 8 cm.) from the linea alba, runs forward (deviating a little outward), dips under the panniculus, passes through a foramen in the abdominal wall about a handbreadth from the median plane, and joins the internal thoracic vein. The external pudic vein (middle mammary vein) is also of considerable size. It ascends in the inguinal canal as a satellite of the artery and joins the external iliac vein. The right and left veins are connected at the posterior border of the base of the udder by a large transverse branch. From the latter arises the perineal vein (posterior mammary vein), which runs medially upward and backward to the perineum, turns around the ischial arch, and joins the internal pudic vein. In the male these veins are relatively small.

The deep veins of the thigh and leg resemble those of the horse, but there is no recurrent tibial vein.

The saphenous vein is much smaller than in the horse.

The recurrent tarsal vein (external saphenous) is large. It is the upward continuation of the external plantar metatarsal vein and anastomoses with the anterior tibial and saphenous veins. It arises on the outer face of the hock, ascends at first in front of the tendo Achillis, then crosses the latter externally, passes up between the biceps femoris and semitendinosus, and joins the posterior femoral vein.

There are three chief metatarsal veins. The great dorsal metatarsal vein arises at the distal part of the metatarsus by the union of the dorsal digital vein and a large branch from the venous arch above the sesamoids. It ascends superficially between the long and lateral extensor tendons and becomes the chief radicle of the anterior tibial vein. The internal plantar metatarsal vein arises from the venous arch above the fetlock, ascends along the inner border of the suspensory ligament, passes through the vascular canal of the metatarsus and centro-tarsal (as the perforating tarsal) and joins the anterior tibial vein. The external plantar metatarsal vein is larger than the preceding. It passes superficially over the outer face of the hock and is continued by the recurrent tarsal vein.

The digital veins differ from those of the fore limb chiefly in that the dorsal vein is large and the plantar absent or small.

The portal vein is formed usually by the confluence of two radicles, gastric and mesenteric. It receives the right gastro-epiploic vein and veins of the pancreas. The gastric vein is the largest affluent. It is formed by the junction of three veins, the left of which receives the splenic vein. The anterior mesenteric vein is also formed by the confluence of three radicles; it usually receives the small posterior mesenteric vein. The portal tributaries are in general satellites of the corresponding arteries.

The Lymph Vessels and Glands

The thoracic duct arises from a small cisterna chyli and is very variable. It is exceptional to find a single trunk throughout, as is often the case in the horse. The duct is largely covered by fat and small lymph glands. There are often two ducts, one on either side of the aorta, which may join at a variable point or terminate close together at the junctions of the jugular and brachial veins. In other cases the duct is single for a variable distance, then bifurcates or divides into three or four branches, which are often connected by plexiform anastomoses.

The efferent vessels from the intestine converge to a large trunk which accompanies the anterior mesenteric artery and vein. It passes below the pancreas and receives usually a large duct which is formed by efferent vessels from the stomach, liver, and spleen; this duct sometimes opens directly into the cisterna. The gastro-intestinal trunk receives the collecting duct (truncus lumbalis) of the lumbar lymph vessels, forms a bend around the right renal vessels, and joins the cisterna.

The lymph glands in the ox are in general less numerous but larger than those of the horse, and in some situations a single large gland occurs instead of a group of smaller ones, as found in the latter animal.

The submaxillary lymph glands are usually two in number, right and left; each is situated under the external maxillary vein between the submaxillary salivary gland and the sterno-cephalicus muscle. Usually one or two hæmolymph glands are near it. There is generally a small gland on the deep face of the anterior part of the submaxillary salivary gland, and small nodes may be found further forward in the submaxillary space.

A large subparotid lymph gland lies on the postero-superior part of the masseter muscle, partly under cover of the upper end of the parotid gland. Several hæmolymph glands lie on its deep face.

The pharyngeal lymph glands number two or three on each side. Of these, two large suprapharyngeal glands (Lg. retropharyngeales) are situated about an inch apart between the dorsal wall of the pharynx and the ventral straight muscles (Figs. 281, 365). These are two to three inches long. Enlargement of them is likely to cause difficulty in swallowing and in respiration. Behind these are several hæmolymph glands. An atlantal gland is situated below the wing of the atlas on the spinal accessory nerve. It is discoid, oval in outline, and may be an inch and a half or more in length. It is partly covered by the upper end of the submaxillary salivary gland.

A smaller lymph gland (parapharyngeal) is usually found along the lower border of the carotid artery (i. e., ventral to the atlantal gland) on the lateral wall of the pharynx and under cover of the submaxillary salivary gland or at its posterior border.

Two or three small anterior cervical lymph glands commonly lie along the carotid artery a little further back.

The middle cervical lymph glands comprise a series of small nodes along the dorsal face of the trachea.

In the sheep and goat there is a lymph gland at the middle of the neck, in the angle between the spinalis and complexus, covered by the splenius. It receives vessels from the atlantal gland and sends efferents to the prescapular gland.

The prescapular or superficial cervical lymph gland is situated at the anterior border of the supraspinatus under cover of the mastoido-humeralis and omo-transversarius. It is elongated and may be an inch or more in width and four or five inches long. Two occur in exceptional cases.

A chain of hæmolymph glands lies along the front of the shoulder, covered above by the trapezius. Others are frequently found (in the calf especially) on the surface of the omo-transversarius at the point where it passes under the mastoido-humeralis (Forgeot).

The posterior cervical or prepectoral lymph glands number commonly three or four on each side. One or two are placed on the brachial vessels, one below the brachial vein at the first rib, and one at the junction of the common trunk of the external and subcutaneous thoracic veins with the brachial.

The intercostal lymph glands are situated, as in the horse, at the upper parts of the intercostal spaces. Associated with them are hæmolymph glands.

The sternal lymph glands are situated along the course of the internal thoracic artery at the lower part of the intercostal spaces. The largest is close to the thoracic inlet. Several glands occur in the fat about the apex of the pericardium.

4. Several anterior mediastinal lymph glands are placed along the œsophagus and the trachea.^[183] Hæmolymph glands occur here also.

Usually three large bronchial lymph glands are present (Fig. 289). One is situated at the origin of each chief bronchus and the third is under the trachea at the origin of the special bronchus of the apical lobe of the right lung. Another may lie between the aorta and the left branch of the pulmonary artery. These glands are often pigmented. Other small nodes are situated on the bronchi within the lungs.

The posterior mediastinal lymph glands comprise two or three of large size placed along the dorsal wall of the œsophagus. There may be a single gland about eight inches (ca. 20 cm.) long, the anterior half of which lies on the œsophagus (Fig. 289).^[184] A small gland is situated in the acute angle formed by the posterior vena cava and the diaphragm.

A single axillary lymph gland is situated on the distal part of the teres major on the course of the vein from the latissimus dorsi.

The lumbar lymph glands form an irregular series scattered along the abdominal aorta and posterior vena. A bean-shaped renal lymph gland occurs at the hilus of each kidney. Hæmolymph glands occur along the course of the aorta.

The internal iliac lymph glands comprise a group of five or six at the termination of the aorta and the origin of the vena cava. A discoid gland, two inches or more in diameter, occurs near the side of the pelvic inlet at the angle of divergence of the circumflex iliac artery from the external iliac. A small gland is sometimes found at the origin of the prepubic artery.

The external iliac lymph glands number commonly two on either side, and are situated near the point of the hip in front of the anterior branch of the circumflex iliac artery.

The superficial inguinal lymph glands are situated centrally below the prepubic tendon and in the narrow space between the origins of the graciles. In the male there are usually two or three on either side of the penis behind the sigmoid flexure. In the cow they are supramammary, i. e., are situated above the posterior margin of the base of the udder; two large glands which are in apposition with each other medially are constant, and above these there are often two smaller glands.

An ischiatic lymph gland, which is discoid and usually about an inch in diameter, is situated on the lower part of the sacro-sciatic ligament near the lesser sciatic notch under cover of the biceps femoris.

An anal lymph gland is situated on the retractor ani on either side.

The gastric lymph glands are numerous and comprise: (1) a chain along the course of the right ruminal artery and two or three in the left groove of the rumen; (2) several on the reticulum above and below the junction with the omasum; (3) a series along the course of the superior omasal vessels and the lesser curvature of the abomasum; (4) an extensive chain along the ventral face of the omasum and the great curvature of the abomasum at the attachment of the great omentum.

Two or three large hepatic or portal lymph glands are found at the upper part of the portal fissure of the liver.

No lymph glands occur at the hilus of the spleen. The efferent vessels from the spleen appear to go to glands along the course of the cœliac artery.

A large discoid cœliac lymph gland lies on the pancreas and the cœliac artery, covering the latter as it gives off its primary branches.

The mesenteric lymph glands are large and numerous. They form a chain in the lower part of the mesentery along the course of the great mesenteric artery. They are chiefly elongated and narrow, and some have a length of six to eight inches (15 to 20 cm.) or more. Sometimes several unite and form a narrow band about two feet in length. A large gland occurs at the origin of the spiral part of the colon, a group is found near the anterior mesenteric trunk, and others are scattered along the coils of the colon, which are best seen on the right side. A chain of small lymph glands extends along the terminal part of the colon and the dorsal face of the rectum.

The precrural lymph gland is situated on the aponeurosis of the external oblique at the anterior border of the tensor fasciæ latæ a short distance above the stifle. It is elongated like the prescapular gland and may be six inches (ca. 15 cm.) long. Several subcutaneous hæmolymph glands occur in this vicinity; others are situated further forward on the flank not far from the last rib. There is usually a round, flattened lymph gland about an inch in diameter on the upper part of the quadriceps femoris under cover of the tensor fasciæ latæ, and one or more small ones occur on the surface of the latter muscle.

No deep inguinal lymph glands are present.

A single popliteal lymph gland an inch or more in length is situated somewhat lower down on the gastrocnemius than in the horse, behind the tibial and peroneal nerves.

CIRCULATORY SYSTEM OF THE PIG

THE HEART

The pericardium is attached to the sternum from a point opposite to the third rib as far as the xiphoid cartilage, and also to the sternal part of the diaphragm.

The heart is small in proportion to the body-weight, especially in fat animals. It is relatively short and wide. The apex is blunt and is marked by a notch (Incisura apicis). Its long axis is more oblique, but it is less asymmetrical with regard to the median plane, than in the horse or ox. The lower border of the left auricle (appendix) is marked by several notches and is situated at a lower level than the right one. The right longitudinal groove is placed far back and there is no posterior sulcus.

The Arteries

The pulmonary vessels present no remarkable features.

The aorta resembles that of the horse and ox in its course and relations, but the arch is more strongly curved. There is no common brachiocephalic trunk (anterior aorta).

The brachiocephalic artery arises first from the aortic arch and passes forward below the trachea to the first rib. Here it gives off the common carotid arteries, and is continued around the first rib as the right brachial.

The superior cervical, vertebral, and dorsal arteries usually arise by a common trunk.

The inferior cervical artery is large; its ascending branch gives off the posterior thyroid artery and parotid branches.

The internal and external thoracic arteries give branches to the pectoral mammary glands; the external may be absent.

The left brachial artery arises from the aortic arch just above the brachiocephalic. It curves forward and downward and turns around the anterior border of the first rib. Its superior cervical, vertebral, and dorsal branches usually arise separately.

The carotid arteries arise from the brachiocephalic close together or by a very short common trunk. They terminate in occipital and internal and external carotid divisions.

The occipital artery resembles that of the horse.

The internal carotid artery usually arises by a common trunk with the occipital. After giving off a large meningeal branch it passes through the foramen lacerum and forms with the opposite artery a rete mirabile which resembles that of the ox, but is smaller and is not connected with the vertebral and condyloid arteries.

The external carotid artery has the same course and termination as in the horse. Its branches present the following special features: (1) The lingual artery is relatively large and supplies the pharyngeal artery, the sublingual, muscular branches, and branches to the soft palate, submaxillary gland, and larynx. (2) The external maxillary artery is small and is distributed chiefly to the submaxillary gland, the pharyngeal lymph glands, the masseter and the panniculus. It does not extend upon the lateral surface of the face. (3) The posterior auricular artery is long and relatively large; it gives off the posterior meningeal.

The internal maxillary artery pursues a flexuous course between the ramus of the mandible and the pterygoid muscles. Its branches offer the following special features: (1) The inferior alveolar (or dental) is large; branches from it emerge through four or five mental foramina and take the place of the inferior labial. (2) The buccinator artery is also large and extends to the lips. (3) The infraorbital artery extends to the snout and replaces the superior labial largely and the lateral nasal in part. The malar branch compensates largely for the absence of the lateral and dorsal nasal. (4) The palatine artery is small.

The intercostal arteries number fourteen to sixteen in either side; of these ten to twelve arise from the aorta, usually by short common trunks. Frequently an intercostal artery is given off from that of an adjacent space.

The bronchial and œsophageal arteries usually arise separately.

The cœliac artery is half an inch to an inch long. It supplies a branch to the left crus of the diaphragm and divides into two primary branches, gastro-hepatic and splenic. The gastro-hepatic artery is the larger. It gives off pancreatic branches, the anterior gastric artery, branches to the lesser curvature of the stomach, pyloric and gastro-duodenal arteries. The latter divides into pancreatico-duodenal and right gastro-epiploic. The anterior gastric usually supplies the œsophageal artery. The continuing trunk (A. hepatica propria) gives off a cystic branch and divides in the portal fissure into four branches which supply the liver. The splenic artery gives off the posterior gastric (usually), branches to the stomach above the cardia, twigs to the pancreas, short gastric arteries to the left part of the great curvature, and splenic branches, and is continued as the left gastro-epiploic artery.

The posterior gastric may arise from the gastro-hepatic or in the angle of divergence of the two primary divisions of the cœliac. The œsophageal branch may come from the splenic.