192 



TR ANSVERS ALIS RECTUS . 



Fig. 79 * 



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 zig-zag lines, 



called lineae transversae. 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 transver- 

 salis, and pyramidalis. By its inter- 

 nal surface with the ensiform carti- 

 lage, the cartilages of the fifth, sixth, 

 seventh, eighth and ninth ribs, with 

 the posterior lamella of the internal 

 oblique, the peritoneum, and the epi- 

 gastric 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 pubis. It is 

 enclosed in the same sheath with the 

 rectus,f 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 forma- 

 tion 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- 



* A lateral view of the trunk of the body, showing its muscles, and particularly the 

 transversalis abdominis. 1. The costal origin of the latissimus dorsi muscle. 2. The 

 serratus magnus. 3. The upper part of the external oblique muscle divided in the 

 direction best calculated to show the muscles beneath without interfering with its in- 

 digitations with the serratus magnus. 4. Two of the external intercostal muscles. 

 5. Two of the internal intercostals. 6. The transversalis muscle. 7. Its posterior 

 aponeurosis. 8. Its anterior aponeurosis forming the most posterior layer of the sheath 

 of the rectus. 9. The lower part of the left rectus with the aponeurosis of the trans- 

 versalis passing in front. 10. The right rectus muscle. 11. The arched opening left 

 between the lower border of the transversalis muscle and Poupart's ligament, through 

 which the spermatic cord and hernia pass. 12. The gluteus maximus, and medius, 

 and tensor vaginae femoris muscles invested by fascia lata. 



t This is not precisely the fact, as there is a separate sheath for the pyramidalis. G. 



