THE POSTERIOR MUSCLES OF THE ABDOMEN 



419 



The parietal portion lines the cavity in varying quantities in different situations. 

 It is especially abundant on the posterior wall of the abdomen, and particularly 

 around the kidneys, where it contains much fat. On the anterior wall of the abdo- 

 men, except in the pubic region, and on the lateral wall above the iliac crest, 

 it is scanty, and here the transversalis fascia is more closely connected with the 

 peritoneum. There is a considerable amount of extraperitoneal connective tissue 

 in the pelvis. 



The visceral portion follows the course of the branches of the abdominal aorta 

 between the layers of the mesenteries and other folds of peritoneum which connect 

 the various viscera to the abdominal wall. The two portions are directly con- 

 tinuous with each other. 



bdominal inguinal 

 ring 



Inf. epigastric artery 



Fia. 401. The abdominal inguinal ring. 



The Deep Crural Arch. Curving over the external iliac vessels, at the spot where 

 they become femoral, on the abdominal side of the inguinal ligaments and loosely 

 connected with it, is a thickened band of fibers called the deep crural arch. It 

 is apparently a thickening of the transversalis fascia joined laterally to the center 

 of the lower margin of the inguinal ligament, and arching across the front of 

 the femoral sheath to be inserted by a broad attachment into the pubic tubercle 

 and pectineal line, behind the inguinal aponeurotic falx. In some subjects this 

 structure is not very prominently marked, and not infrequently it is altogether 

 wanting. 



2. The Posterior Muscles of the Abdomen. 



Psoas major. 

 Psoas minor. 



Iliacus. 



Quadratus lumborum. 



The Psoas major, the Psoas minor, and the Iliacus, with the fasciae covering 

 them, will be described with the muscles of the lower extremity (see page 466). 



The Fascia Covering the Quadratus Lumborum. This is a thin layer attached, 

 medially, to the bases of the transverse processes of the lumbar vertebrae; below, 



