THE ABDOMINAL FASCL# AND MUSCLES 287 
Passing downward and forward, its fibers spread out and join the tendinous center. 
The left crus arises by a thin tendon from the ventral longitudinal ligament at the 
first and second lumbar vertebre. 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 lumbo-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 ven cave, which is encircled by fibers. A strong tendinous layer extends 
across below the hiatus cescphageus. 
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 mediale dextrum 
and a crus 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 vertebre. It transmits the cesophagus, the vagus nerves, 
and the cesophageal branch of the gastric artery. (8) The foramen vene cave’ 
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 vertebre. The vena cava is firmly attached to the margin of the 
opening.® 
Relations—The thoracic surface is related to the endothoracic fascia, pleure, 
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 FASCIZ AND MUSCLES 
(FASCLE 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 flank 
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 ven cave from the vertebral column vary according to the ful- 
ness of the abdominal viscera and the degree of contraction of the diaphragm. The statements 
given above are averages. 
