. Cunningham's Text-book of anatomy. Anatomy. 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
. Cunningham's Text-book of anatomy. Anatomy. 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 d inguinal ring, placed half an inch above E 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 .. » ,? i • r- j i. ,i_ p . (1.) iii the thorac
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