RECTUS. PYRAMIDALIS. 217 



mellae ; anterior, which is attached to the bases of the transverse pro- 

 cesses of the lumbar vertebrae ; middle, to the apices of the transverse 

 processes ; and posterior, to the apices of the spinous processes. The 

 anterior and middle lamellae enclose the quadratus lumborum muscle ; 

 and the middle and posterior, the erector spinae. The union of the 

 posterior lamella of the transversalis with the posterior aponeurosis of 

 the internal oblique, serratus posticus inferior, and latissimus dorsi, 

 constitutes the lumbar fascia. 



Relations. By its external surface with the internal oblique, the in- 

 ternal surfaces of the lower ribs, and internal intercostal muscles. By 

 its internal surface with the transversalis fascia, which separates it from 

 the peritoneum, with the psoas magnus, and with the lower part of the 

 rectus and pyramidalis. The spermatic cord and oblique inguinal 

 hernia pass beneath the lower border, but have no direct relation 

 with it. 



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

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

 the front of the os pubis. The sheath may then be dissected off and 

 turned to either side ; this is easily done excepting at the lineae trans- 

 versse, where a close adhesion subsists between the muscle and the ex- 

 ternal 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 zig-zag intersections, 

 called lineae transversae. One of these is usually situated at the um- 

 bilicus, 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 

 aponeurosis of the internal oblique, below with the aponeurosis of the 

 transversalis, and pyramidalis. By its internal surface with the 

 ensiform cartilage, the cartilages 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 lamella of the internal oblique, and behind by the poste- 

 rior lamella of the internal oblique and the aponeurosis of the trans- 

 versalis. At the commencement of the lower fourth, the posterior 



