130 DK PETER THOMPSON. 



There can 1)3 little doubt, therefore, that the upper and 

 lower fasciae of the levator ani in man correspond to the upper 

 and lower fascia of the flexor group of tail muscles in other 

 mammals, and it now becomes necessary to explain the apparent 

 differences in their lateral pelvic attachments. An examination 

 of the obturator fascia in man will simplify the subsequent 

 description. 



The obturator fascia is regarded as the special fascia of the 

 obturator internus; it covers the inner surface of the muscle, 

 and at its limits obtains' attachment to the bone.~/ Above, it 

 extends to the iliac portion of the ilio-pectineal line ; in front, 

 it is attached to the back of the body of the pubis ; behind, it 

 reaches beyond the muscle to the great sacro-sciatic ligament ; 

 and below, it joins the falciform process of the latter, and thus 

 gains attachment to the ascending ramus of the ischium and the 

 descending ramus of the pubis. 



By the attachment of the levator ani, the fascia on the 

 lateral pelvic wall is divisible into two parts, an upper 

 pelvic portion lined by peritoneum, and a lower perineal 

 portion forming the outer boundary of the ischio-rectal fossa. 

 These divisions are named by His^ the pars supradiaphrag- 

 matica and the pars infradiaphragmatica of the fascia obtura- 

 toria. But other considerations lead one to regard the division 

 as being based on something more than a muscular attachment. 

 The two parts have a different appearance, and are not of equal 

 thickness. The pelvic portion is thicker, more aponeurotic and 

 less transparent than the perineal portion, which is thinner 

 and more membranous, allowing the underlying muscular fibres 

 to be seen through it (PI. XII.). 



In those mammals which 1 have had the opportunity of dis- 

 secting, I have not been able to find any corresponding arrange- 

 ment of the fascia on the lateral wall of the pelvis except in 

 the orang-utan, in which the condition very closely resembles 

 that in man, though there is one important point of difference, 

 tlie significance of which will be referred to subsequently. 

 Almost invariably the fascia is of uniform thickness, and 

 is not divisilde into two parts, even by the attachments of the 



1 His, W., Die. Anatomi&clie Nomendalar {Nomina Anaiomica), Leipzig, 1895, 

 p. 142. 



