THE ABDOMINAL MUSCLES 245 



center. It is situated a little to the left of the median plane and two or three 

 inches below the thirteenth thoracic vertebra (in expiration). It transmits the 

 oesophagus, the vagus nerves, and the oesophageal branch of the gastric artery. 

 (3) The foramen venae cavae (s. dextrum) pierces the tendinous center about an 

 inch to the right of the median plane, and about six inches below the twelfth 

 thoracic vertebra (in ex]iiration). The vena cava is firmly attached to the 

 margin of the opening.' 



Relations. — The thoracic surface is related to the endothoracic fascia, pleura^, 

 pericardium, the bases of the lungs, and the ribs in part. The abdominal surface 

 is in great part covered by the peritoneum, and is related chiefly to the liver, stom- 

 ach, spleen, pancreas, kidneys and adrenals, and the anterior flexures of the colon. 

 The sympathetic and splanchnic nerves pass between the crus and the psoas muscles 

 on each side. The asternal vessels perforate the edge of the muscle at the ninth 

 costo-chondral joint. 



Blood-supply. — Phrenic and asternal arteries. 



Nerve-supply. — Phrenic nerves (from the fifth, sixth, and seventh cervical 

 nerves) . 



The Abdominal Muscles 



The superficial fascia covering the lateral and ventral walls of the abdomen is 

 continuous dorsally with the lumbo-dorsal fascia, in front with the thoracic fascia, 

 and behind with the gluteal fascia. In the inguinal region it forms part of the 

 fascia of the penis or of the mammary glands. At the lower part of the flank it 

 forms a fold which is continuous with the fascia of the thigh near the stifle joint. 

 In this fold are the precrural lymph-glands. Medially it blends with the linea alba. 

 It contains the abdominal portion of the panniculus carnosus. 



The abdominal panniculus (M. cutaneus maximus) covers a large part of 

 the lateral surface of the abdomen and thorax. The general direction of its 

 fibers is longitudinal. Its posterior extremity forms the basis of the fold of the 

 flank. Its anterior extremity is inserted by a thin tendon into the internal tuber- 

 osity of the humerus, with the posterior deep pectoral muscle. Its dorsal edge may 

 be indicated by a line drawn from the upper end of the thirteenth rib to the fold of 

 the flank. Its ventral limit corresponds to a line drawTi from the fold to a point 

 about a hand-breadth external to the umbilicus, and from here to a point a little 

 above the level of the elbow. Behind the shoulder the fibers become oblique and 

 blend with the scapular portion. The aponeurosis extends ventrally to the linea 

 alba, dorsally to the supraspinous ligament. The muscle is intimately adherent 

 to the skin, so that special care is necessary in removing the latter. Its deep face, 

 on the other hand, is loosely attached to the underlying structures by a quantity of 

 areolar tissue which is more or less loaded with fat (panniculus adiposus) in animals 

 in good condition. The large external thoracic (" spur ") vein is partially embedded 

 in the lower part of the muscle. Its action is to twitch the skin. 



The deep fascia is represented chiefly by the abdominal tunic (Tunica flava 

 abdominis) . This is a sheet of elastic tissue which assists the muscles in supporting 

 the great weight of the abdominal viscera. It is practically coextensive with the 

 obliciuus externus, which it covers. Ventrally it is thick, and is intimately ad- 

 herent to the aponeurosis of the muscle. Laterally it becomes thinner and is 

 more easily separated, although fibers from it dip in between the muscle-bundles. 

 It is continued for some distance upon the intercostals and serratus magnus. 



^In order to get a clear idea of the relative positions of these foramina and of the form of 

 the diaphragm, the thoracic surface of the hitter should be examined while the alxlominal viscera 

 remain in situ. 



