162 



ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



The rectus and pyramidalis, like the other muscles of the anterior abdominal wall, are innervated by branches of 

 the lower intercostal nerves; the flat abdominal muscles also receive branches from the iliohypogastric and the ilio- 

 inguinal nerves from the lumbar plexus. The cremaster muscle is supplied by the external spermatic nerve (the genital 

 branch of the genitocrural nerve). 



When all the anterior abdominal muscles act together their function is to diminish the size of the abdominal cavity 

 and to compress the abdominal contents, the increased intra-abdominal tension aiding in the evacuation of the contents of 

 the intestines, of the uterus, and possibly also of the urinary bladder. With the exception of the transversus abdominis, 

 these muscles also draw the thorax downward, the rectus directly downward, and the obliqui, when acting separately, 

 toward the side of the contracting muscle. When the thorax is fixed, the anterior abdominal muscles and particularly 

 the rectus, raise the pelvis. 



THE POSTERIOR ABDOMINAL MUSCLE. 



The quadratus lumborum (Figs. 251 and 254) is a flattened, rather thick, and approxi- 

 mately quadrilateral muscle which forms a portion of the posterior abdominal wall. It extends 



Lumbocostal ligament 



Thoracic vertebra XII 



Lumbar vertebra I ■ 



Tweljth rib 



Lumbar vertebra V — 



Iliolumbar ligament 

 .KrG. 251. — The quadratus lumborum seen from the side and somewhat from behind (diagrammatic;. 



between the crest of the ilium and the twelfth rib, and consists of two incompletely separated layers, 

 a posterior and an anterior. The posterior portion (Fig. 251) arises by aponeurotic fibers from 



