Part 191

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.

FIG. 480.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF PIG, ANTERIOR VIEW.

a, Terminal part of volar interosseous artery; b, dorsal interosseous artery; c, rete carpi dorsale; d, dorsal metacarpal arteries; e, dorsal common digital arteries; f, dorsal proper digital arteries. ]

FIG. 481.—ARTERIES OF DISTAL PART OF RIGHT FORE LIMB OF PIG, POSTERIOR VIEW.

g, Ulnar artery; h, superficial branch of radial artery; i, collateral ulnar artery; j, volar interosseous artery; h, deep branch of radial artery; k, deep volar metacarpal arteries; l, superficial volar metacarpal arteries; m, volar common digital artery; n, volar proper digital arteries. ]

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.