THE ABDOMINAL FASCIiE AND MUSCLES 287 



Passing downward and forward, its fibers spread out and join the tendinous center. 

 The left cms arises by a thin tendon from the ventral longitudinal ligament at the 

 first and second lumbar vertebrae. This is succeeded by a triangular belly which 

 joins the central tendon. Between the crura and the attachment to the last rib 

 the edge of the muscle crosses the ventral surface of the psoas muscles without at- 

 tachment, forming the so-called liunbo-costal arch (Arcus lumbocostalis) ; here the 

 thoracic and abdominal cavities are separated only by the serous membranes and 

 some areolar tissue. The tendinous center (Centrum tendineum) resembles the 

 periphery in outline, but is more elongated. It is partially divided into right and 

 left parts by the descent of the crura into it. It is composed largely of radiating 

 fibers, but many interlace in various directions; this is specially evident around the 

 foramen venae cavse, which is encircled by fibers. A strong tendinous layer extends 

 across below the hiatus oescphageus. 



Schmaltz and others describe the lumbar part as consisting of four crura, two medial and two 

 lateral. On this basis the left crus of the preceding description becomes the crus laterale sinistrum, 

 and the corresponding part of the right side is the crus laterale dextrum. The central part is divided 

 by the hiatus cesophageus and the slit which extends from it dorsally into a crus medlale dextrum 

 and a cms mediale sinistrum. Both modes of division are in part artificial. 



The diaphragm is pierced by three foramina. (1) The hiatus aorticus is an 

 interval between the two crura and below the last thoracic vertebra. It contains 

 the aorta, vena azygos, and cisterna chyli. (2) The hiatus cesophageus^ perforates 

 the right crus near its junction with the tendinous center. It is situated a little to 

 the left of the median plane and about a hand breadth ventral to the thirteenth 

 and fourteenth thoracic vertebrae. It transmits the oesophagus, the vagus nerves, 

 and the oesophageal branch of the gastric artery. (3) The foramen venae cavse- 

 pierces the tendinous center about an inch (ca. 2-3 cm.) to the right of the median 

 plane, and about six to eight inches (ca. 15-20 cm.) below the eleventh and 

 twelfth thoracic vertebrae. The vena cava is firmly attached to the margin of the 

 opening.' 



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

 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, intestine, spleen, pancreas, kidneys, and adrenals. The sympathetic trunk and 

 splanchnic nerve pass between the crus and the psoas muscles on each side. The 

 musculo-phrenic vessels perforate the edge of the muscle at the ninth costo-chondral 

 joint. 



Blood-supply. — Phrenic and musculo-phrenic arteries. 



Nerve-supply. — Phrenic nerves. 



The Abdominal Fasci.s: and Muscles 

 (fascia et musculi abdominis) 



The superficial fascia of the abdomen is in part fused dorsally with the lumbo- 

 dorsal fascia; in front it is continuous with the superficial fascia of the shoulder and 

 arm, behind with that of the gluteal region. In the inguinal region it forms part 

 of the fascia of the penis or of the mammary glands. At the lower part of the flaiik 

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



1 Formerly termed the foramen sinistrum. ^ Formerly termed the foramen dextrum. 



' 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 latter should be examined in properly preserved sub- 

 jects while the abdominal viscera remain in situ. It will be observed that the distances of the 

 hiatus cesophageus and foramen vena; cavas from the vertebral column vary accordmg to the ful- 

 ness of the abdominal viscera and the degree of contraction of the diaphragm. The statements 

 given above are averages. 



