Part 72

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.

The =anterior mesenteric artery= is long like that of the ox. It gives twigs to the pancreas, the ilio-cæcal and two colic arteries, and is continued in the mesentery as the artery of the small intestine. This gives off numerous branches which form a series of arches along the mesenteric lymph glands. From these is formed a rich network which gives off innumerable fine branches placed close together. The colic arteries enter the axis of the spiral coil of the colon and anastomose at its apex. Their branches also form rich networks.

A =phrenico-abdominal artery= arises on either side a little in front of the renals. It divides into branches which go to the costal part of the diaphragm and the abdominal muscles.

The =renal= and =spermatic arteries= present no special characters.

The =posterior mesenteric artery= arises near the termination of the aorta. It is small and is distributed like that of the ox.

Six pairs of =lumbar arteries= arise from the aorta. The seventh comes from the middle sacral.

The terminal branches of the aorta resemble those of the ox.

The arteries of the shoulder, arm, and forearm resemble in general those of the ox.