134 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



scarcely developed in any other animal (Fig. 107). In the orang, 

 for instance, also an upright primate, the external oblique has no 

 attachment to the crest of the ilium, and takes no part in forming 

 the outer part of Poupart's ligament (Fig. 107), but its tendon 

 terminates over and strengthens the region of the inguinal canal. 

 This is the usual termination in the mammalia. 



(2) The internal oblique and transversalis (conjoined parts) in 

 the orang, and in all primates except man, arise from the firm 

 tubular sheath of the ilio-psoas, also from the extensive anterior 

 border of the ilium, and arching over the spermatic cord end in 

 a long insertion on the ileo-pectineal line. They act as a 

 powerful compressor or sphincter of the inguinal canal, and thus 

 prevent hernia (Fig. 107.6). 



(3) The human manner of walking, and the great head of the 

 human child at birth require a wide pelvis. All mammals 



nt. sup. sp. 

 Pouparts lig. int ob - 



tendon ofext 

 ob. cut 



rectus 



muscular) 

 comp. j 



vascular 



conjoined 

 muscle. 



inguinal canal. 



Fio. 107.—^. Poupart's Ligament and the Crural Passage of Man. 



B. Poupart's Ligament, Crural Passage, and sphincter-like Conioined 

 Muscle of the Orang. 



adapted to the prone posture have a narrow pelvis, and hence a 

 narrow anterior abdominal wall (Figs. 106.4 and B) through 

 which the inguinal canal passes very obliquely. The course of 

 the canal is more direct in man, and therefore offers a greater 

 facility to the escape of the abdominal contents. 



(4) The size of the space between the edge of the pelvis and 

 Poupart's ligament (the crural passage) is very much greater in 



