288 FASCIvB AND MUSCLES OF THE HOESE 



In this fold are the prefemoral lymph-glands. Medially it blends with the hnea 

 alba. It contains the abdominal cutaneous muscle (described on p. 254). 



The deep fascia is represented chiefly by the abdominal tunic (Tunica flava 

 abdominis) . This is a sheet of elastic tissue which assists the muscles in supporting 

 the great weight of the abdominal viscera. It is practically coextensive with the 

 obliquus externus, which it covers. Ventrally it is thick, and is intimately ad- 

 herent to the aponeurosis of the muscle. Laterally it becomes thinner and is more 

 easily separated, although fibers from it dip in between the muscle-bundles. It is 

 continued for some distance upon the intercostals and serratus ventrahs. Traced 

 forward, it passes as a thin layer beneath the posterior deep pectoral muscle. Pos- 

 teriorly it is attached to the tuber coxae. In the inguinal region it forms the deep 

 fascia of the prepuce or of the mammary glands. 



The linea alba is a median fibrous raphe which extends from the xiphoid car- 

 tilage to the prepubic tendon. It is formed chiefly by the junction of the aponeu- 

 roses of the obhque and transverse muscles, but partly by longitudinal fibers. A 

 little behind its middle (about in a transverse plane tangent to the last pair of ribs) 

 is a cicatrix, the umbilicus, which indicates the position of the umbihcal opening 

 of the foetus. 



1. Obliquus abdominis externus. — This is the most extensive of the abdominal 

 muscles. It is a broad sheet, irregularly triangular in shape, widest behind. Its 

 fibers are directed chiefly downward and backward. 



Origin. — (1) The lateral surfaces of the last fourteen ribs, and the fascia over 

 the external intercostal muscles; (2) the lumbo-dorsal fascia. 



Insertion. — (1) The linea alba and the prepubic tendon; (2) the tuber coxte and 

 shaft of the ilium ; (3) the medial femoral fascia. 



Action. — (1) To compress the abdominal viscera, as in defecation, micturition, 

 parturition, and expiration; (2) to flex the trunk (arch the back) ; (3) acting singly, 

 to flex the trunk laterally. 



Structure. — The muscle is composed of a muscular part and an aponeurosis. 

 The muscular part lies on the lateral wall of the thorax and abdomen. It arises 

 by a series of digitations, the anterior four of which alternate with those of the ser- 

 ratus ventralis. The origin may be indicated by a slightly curved line (concave 

 dorsally) drawn from the lower part of the fifth rib to the tuber coxee. The fibers 

 are directed downward and backward and terminate on the aponeurosis, except in 

 the upper part of the flank, where they are less oblique in direction and end on the 

 tuber coxae. The line of junction is a curve (concave dorsally) extending from the 

 upper edge of the posterior deep pectoral muscle toward the point of the hip. The 

 aponeurosis is intimately attached to the abdominal tunic, and its fibers are largely 

 interwoven ventrally with those of the aponeurosis of the internal oblique. By 

 this fusion is formed the outer sheath of the rectus abdominis, which blends at the 

 linea alba with that of the opposite side. In the inguinal region the aponeurosis 

 divides into two chief layers; one of these curves dorsally and backward and is in- 

 serted into the tuber coxae and the prepubic tendon. Between these points the 

 aponeurosis is much strengthened and is called the inguinal ligament (Ligamentum 

 inguinale). 1 This curves upward and somewhat forward, becomes thin, and blends 

 with the iliac fascia. It forms the posterior wall of the inguinal canal. About an 

 inch (ca. 2 to 3 cm.) in front of the pubis and about two inches (ca. 4 to 5 cm.) 

 from the median plane the aponeurosis is pierced by a slit-like opening, the 

 subcutaneous or external inguinal ring (Annulus inguinalis subcutaneus).^ This is 



1 Also commonly known as Poupart's ligament — based on a false historical allusion. It is 

 in no proper sense a ligament, but is the inguinal part of the aponeurosis of the obliquus externus; 

 ii might therefore well be termed the lamina inguinalis. 



2 It is narrow and slit-Uke in the natural condition, but may appear oval in the dissecting- 

 room, especially if the hind Umb is drawn back and abducted. 



