MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 53 



vertically, while the rest follow in an intermediate direction. They all 

 end on the aponeurosis of insertion of the external oblique. This is an 

 extensive membranous lamina whose origin can be followed along a 

 line which, beginning in front of the fourth or fifth chondrocostal 

 junction, passes distally, diverging gradually from the rectus abdom- 

 inis. At approximately midway between the umbilicus and the pubis 

 it turns rather sharply laterally to reach the dorsal margin of the 

 muscle. The fibers of these aponeurosis have the same orientation as 

 the fleshy elements which they continue. They end on the mid- 

 abdominal line, the pubis, and the ilium. 



The iliac insertion takes place on the outer lip of the acetabular 

 border, from the ventral end of the crest to the origin of the sartorius 

 and tensor fasciae latae. There is at the first point a cranially project- 

 ing pyramidal process upon which the broad abdominal muscles are 

 anchored: (1) the external oblique inserts on, and the internal oblique 

 and transversus abdominis arise from its lateral border, (2) the 

 thoracolumbar fascia and the sacrospinalis muscle are attached behind, 

 (3) m. iliacus arises from its anterior surface, and (4) the quadratus 

 lumborum and iliolumbar ligament end medially. I have not found 

 this spine described in previous pertinent works (Hill, 1962; Straus, 

 1929; Waterman, 1929). In one of my 14-rib males the posterior fleshy 

 fibers of the external oblique reach this process. 



The pubic insertion of the external oblique is arranged into medial 

 and lateral crura, and in two of the males a ligamentum reflexum was 

 clearly seen. Fibers of the medial crus attach to the pubic symphysis, 

 pubic crest, and the medial end of the iliopectineal line. Those of the 

 lateral crus end over the laterally remaining part of the linea Uiopec- 

 tinea up to about the iliopubic junction. At this point the line is well 

 marked, presenting sometimes a short, blunt process that may be the 

 homologue of the pubic tubercle. In the male the two crura are sepa- 

 rated by a wide and oval superficial inguinal ring, of 2 x 1 cm. approxi- 

 mately. It is smaller in the female. The fibers of the crura meet below^ 

 the cord, thus completely encircling the ring. The ligamentum reflexum 

 appears as a flat fibrous bundle behind the medial crus. 



Between the pubic and iliac endings the caudal free border of the 

 external oblique aponeurosis of insertion bridges over the femoral 

 sheath, and more laterally over the iliac fascia. To both of these 

 membranous laminae the external oblique aponeurosis has some de- 

 gree of fusion, but does not form an inguinal ligament. I could not 

 demonstrate the presence of a lacunar ligament. 



All other fibers of the aponeurosis reach the midventral line of the 

 abdomen where they intercross, forming a linea alba along the ap- 

 posed medial margins of the two abdominal recti. 



