THE MUSCLES OF THE ABDOMINAL WALL. 



483 



the aponeurosis of the transversus muscle, passes behind the rectus, and constitutes 

 the posterior lamina of its sheath. This arrangement obtains in the superior three- 

 fourths of the abdominal wall; Below the level of the iliac crest the sheath of the 

 muscle is deficient posteriorly, and a crescentic border, the linea semicircularis 

 (semilunar fold of Douglas), marks the inferior limit of the posterior lamina. In 

 consequence, the rectus in the lower fourth of the abdominal wall rests directly 

 upon the fascia transversalis. Close examination, however, usually reveals a thin 

 layer behind the muscle in continuity with the fold of Douglas, and merging below 

 with the fascia transversalis. In this region the rectus is covered anteriorly by the 

 falx aponeurotica inguinalis of the obliquus internus and transversus, and by the 

 aponeurosis of the obliquus externus, 

 which gradually separates from the 

 subjacent aponeurosis. The superior 

 part of the rectus, lying on the chest 

 wall, is only covered anteriorly by a 

 single layer of aponeurosis derived 

 from the obliquus externus, which in 

 this situation is giving origin to the 

 pectoralis major muscle. 



Canalis Inguinalis. Inguinal 

 canal. The spermatic funiculus in 

 the male, and the round ligament in 

 the female, in their passage through 

 the inferior part of the abdominal wall, 

 pass through the inguinal canal, which 

 is bounded by these abdominal mus- 

 cles. The canal begins at the abdominal 

 inguinal ring, placed half an inch above 

 the inguinal ligament, and midway 

 between the anterior superior iliac 

 spine and the symphysis pubis. It 

 ends at the subcutaneous inguinal ring, 

 placed above the tubercle and crest of 

 the pubis. The anterior wall of the 

 canal is formed by the aponeurosis of 

 the obliquus externus, and in its lateral 

 part by the muscular fibres of the 

 obliquus internus ; the posterior wall 



T . ,.' , , . (I*) In the thoracic wall; II.) In the superior three- 



the Canal IS tormed by the taSCia quarters of the abdominal wall ; (III.) In the inferior 



transversalis, and in its medial part by fourth of the abdominal wall, 

 the falx aponeurotica inguinalis ; while A ' RECTUS MUSCLE; B, OBLIQUUS EXTERNUS; c, DIA 

 the floor of the canal is formed by the 

 inguinal ligament, and in its medial 

 part by the lacunar ligament. The 

 spermatic funiculus, piercing the trans- 

 versalis fascia, enters the inguinal canal 

 at the abdominal inguinal ring, and is there invested by its first envelope, the 

 infundibulifonn or internal spermatic fascia, a sheath of fascia derived from the 

 margins of the ring and continuous with the fascia transversalis. It then passes 

 obliquely medially, downwards, and forwards, and escapes below the inferior border 

 of the obliquus internus muscle, from which it carries off a second investment, 

 partly fascial, partly muscular, the cremaster muscle or cremasteric fascia. Con- 

 tinuing its course, in front of the falx inguinalis, it emerges through the sub- 

 cutaneous inguinal ring, from the edges of which the intercolumnar fascia is 

 derived, the tJiird or external investment for the funiculus. 



Hesselbach's triangle, bounded below by the line of the inguinal ligament, 



i medially by the rectus abdominis muscle, and laterally by the inferior epigastric 



i artery, coursing upwards and medially beneath the fascia transversalis on the medial 



side of the abdominal inguinal ring, is the site of one form of inguinal hernia. 



32 a 



FIG. 429. THE SHEATH OF THE RECTUS ABDOMINIS 

 MUSCLE. 



PHRAGM ; D, OBLIQUUS INTERNUS ; E, TRANSVER- 

 SUS ABDOMINIS. a, Anterior layer of rectus sheath ; 

 b, Fifth costal cartilage ; c, Sixth costal cartilage ; 

 d, Xiphoid process; e, Posterior layer of rectus 

 sheath ; /, Fascia transversalis 



Linea alba. 



Peritoneum ; h, 

 1, Inferior epigastric artery 



