The Heart

Circulatory System of the Pig

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.

The main facts as to the metacarpal and digital arteries are as follows: The rete carpi dorsale is formed essentially by the terminals of the interosseous artery of the forearm. It gives rise to three dorsal metacarpal arteries which descend in the corresponding interosseous spaces and unite with branches of the volar metacarpals to form three common digital arteries. Each of these divides into two proper digital arteries, which descend along the interdigital surfaces of the digits. On the volar surface are two volar arches, superficial and deep, from which three superficial and three deep volar metacarpal arteries arise. The deep arteries unite near the distal end of the space between the principal metacarpal bones to form a stem which unites with the middle (third) superficial artery. The superficial arteries unite to form an arch from which proper digital arteries are given off to the axial aspect of the small digits, and a common digital which supplies two volar proper digital arteries to each of the chief digits.

The arteries of the hip, thigh, and leg are arranged much as in the ox. A few special features may be noted.

The ilio-lumbar artery gives off a branch to the quadriceps femoris. It may also supply the posterior abdominal artery, which otherwise arises from the deep femoral.

The deep femoral artery is given off above the level of the pubis. The posterior abdominal and external pudic arteries may arise from it by a short common trunk or separately. The external pudic gives branches to the prepuce but not to the penis. The popliteal artery gives off the peroneal.

The femoral artery gives off a short trunk which divides into anterior femoral and external circumflex arteries, the latter being much the larger.

The saphenous artery is large. It descends on the inner surface of the leg and hock and concurs with the perforating tarsal artery in forming the proximal plantar arch.

The posterior tibial artery is small, being replaced distally by the saphenous. It gives branches to the muscles on the posterior face of the tibia and supplies the nutrient artery of that bone.

The anterior tibial artery is continued as the dorsalis pedis on the flexion surface of the tarsus. This gives off the perforating tarsal artery, which passes back through the vascular canal of the tarsus and unites with the terminal branches of the saphenous to form the proximal plantar arch.

The metatarsal and digital arteries resemble in arrangement the corresponding vessels of the fore limb.

The Veins

The veins resemble in general those of the ox. Thus there is a hemiazygos vein and two jugular veins, the internal one being relatively larger than in the ox. A few differential features may be noted.

The buccinator vein resembles that of the horse, and unites with the vena reflexa to form a short common trunk which joins the facial.

The facial vein resembles in general that of the horse. The dorsal nasal vein is large, receives the veins from the snout, runs backward in the groove of the nasal bone and joins the frontal vein; it is connected with its fellow by a transverse branch, and anastomoses freely with the malar and facial.

The veins of the distal parts of the limbs naturally present differences which are correlated with those of the arteries.

The Lymph Vessels and Glands

The thoracic duct often divides near its termination into two branches which unite to form an ampulla. The latter suddenly contracts and opens into the terminal part of the left jugular vein.

The submaxillary lymph glands are situated in the space between the omo-hyoid and internal pterygoid muscles in relation to the lower part of the anterior border of the submaxillary salivary gland. There are commonly two on each side, one large, the other small.

The parotid lymph glands (Fig. ) are reddish-brown in color. There are usually four of considerable size on either side. One is situated at the upper part of the posterior border of the masseter, partly covered by the parotid gland. Another large subparotid gland lies below the base of the ear. Ventral to this are two smaller glands, one above and one below the external jugular vein.

The pharyngeal (or retropharyngeal) lymph glands (Fig. ) are situated on the dorsal wall of the pharynx above the external carotid artery and below and behind the paramastoid process. There are usually two of considerable size on either side.

The middle cervical lymph glands form a group on the mastoido-humeralis on the course of the external jugular vein.

The prescapular lymph glands are situated at the anterior border of the anterior deep pectoral muscle undercover of the trapezius and omo-transversarius.

The prepectoral lymph glands are reddish in color and usually three in number. The largest is placed centrally under the trachea; the others are situated on the brachial vessels as they turn around the first rib.

The axillary lymph glands are usually absent, but very small nodes may be found near the insertion of the latissimus dorsi. Cubital glands are not present.

The thoracic lymph glands comprise: (1) a gland of considerable size on the first segment of the sternum; (2) about half a dozen reddish glands along the upper face of the thoracic aorta; (3) several glands along the lower face of the trachea; (4) the bronchial lymph glands; one of these lies on the bifurcation of the trachea and another at the apical bronchus of the right lung (Fig. ).

The lumbar lymph glands are scattered along the abdominal aorta and the vena cava. Those placed near the hilus of the kidney are often designated renal.

The internal iliac lymph glands are rounded and relatively large. They comprise: (1) three or four glands situated on and between the origin of the circumflex iliac and the external and internal iliac arteries; (2) a gland in the angle of divergence of the internal iliac arteries.

The external iliac lymph glands are small, two or three in number, and lie in front of the circumflex iliac vessels near the point of the hip.

The visceral lymph glands of the abdomen comprise:

1. Gastric lymph glands on the lesser curvature of the stomach.

2. Several small hepatic lymph glands along the portal vein.

3. An elongated splenic lymph gland on the splenic vessels near the dorsal end of the spleen.

4. A series of mesenteric lymph glands situated along the anastomotic arches formed by the vessels of the small intestine.

5. Several cæcal lymph glands situated along the first part of the cæcal vessels.

6. Two series of colic lymph glands which accompany the arteries of the spiral part of the colon, and are exposed by separating the coils of the bowel. Small glands are placed in the colic mesentery and above the rectum.

7. The anal lymph glands are situated on either side on the retractor ani.

A small ischiatic lymph gland is found on the sacro-sciatic ligament near the lesser sciatic notch.

The precrural lymph glands are situated on the aponeurosis of the external oblique below the external angle of the ilium.

The superficial inguinal lymph glands are situated behind the external inguinal ring. No deep inguinal lymph glands are present.

The popliteal lymph glands are small normally and may escape notice.

A few nodules occur in front of the distal part of the tendo Achillis.