216 MUSCLES OF THE ABDOMEN. 



To dissect the rectus muscle, its sheath should be opened by a vertical 

 incision extending from over the cartilages of the lower ribs to the front 

 of the os pub is. The sheath may then be dissected off and turned to either 

 side ; this is easily done excepting at the lineae transversae, where a close 

 adhesion subsists between the muscle and the external boundary of the 

 sheath. The sheath contains the rectus and pyramidalis muscle. 



The RECTUS MUSCLE arises by a flattened tendon from the crest of the 

 os pubis, and is inserted into the cartilages of the fifth, sixth, and seventh 

 ribs. It is traversed by several tendinous zigzag intersections, called 

 lineae transverse. One of these is usually situated at the umbilicus, two 

 above that point, and sometimes one below. They are vestiges of the 

 abdominal ribs of reptiles, and very rarely extend completely through the 

 muscle. 



Relations. By its external surface with the anterior lamella of the apo- 

 neurosis of the internal oblique, below with the aponeurosis of the trans- 

 versalis, and pyramidalis. By its internal surface with the ensiform carti- 

 lages of the fifth, sixth, seventh, eighth and ninth ribs, with the posterior 

 lamella of the internal oblique, the peritoneum, and the epigastric artery 

 and veins. 



The PYRAMIDALIS MUSCLE arises from the crest of the os pubis in front 

 of the rectus, and is inserted into the linea alba at about midway between 

 the umbilicus and the os pubis. It is enclosed in the same sheath with 

 the rectus, and rests against the lower part of that muscle. This muscle 

 is sometimes wanting. 



The rectus may now be divided across the middle, and the two ends 

 drawn aside for the purpose of examining the mode of formation of its 

 sheath. 



The sheath of the rectus is formed in front for the upper three-fourths of 

 its extent, by the aponeurosis of the external oblique and the anterior la- 

 mella of the internal oblique, and behind by the posterior lamella of the 

 internal oblique and the aponeurosis of the transversalis. At the com- 

 mencement of the lower fourth, the posterior wall of the sheath terminates 

 in a thin curved margin, the aponeurosis of the three muscles passing alto- 

 gether in front of the rectus. 



The next two muscles can be examined only when the viscera of the 

 abdomen are removed. To see the quadratus lumborum, it is also neces- 

 sary to divide and draw aside the psoas muscle and the anterior lamella 

 of the aponeurosis of the transversalis. 



The QUADRATUS LUMBORUM muscle is concealed from view by the an- 

 terior lamella of the aponeurosis of the transversalis muscle, which is in- 

 serted into the bases of the transverse processes of the lumbar vertebrae. 

 When this lamella is divided, the muscle will be seen arising from, the last 

 rib, and from the transverse processes of the four upper lumbar vertebrae. 

 It is inserted into the crest of the ilium and ilio-lumbar ligament. If the 

 muscle be cut across or removed, the middle lamella of the transversalis 

 will be seen attached to the apices of the transverse processes ; the qua- 

 dratus being enclosed between the two lamellae as in a sheath. 



Relations. Enclosed in the sheath formed by the transversalis muscle, 

 it is in relation in front, with the kidney, the colon, the psoas magnus and 

 the diaphragm. Behind, but also separated by a sheath, with the erector 

 spinae. 



The PSOAS PARVUS arises from the tendinous arches and intervertebral 



