ARRANGEMENT OF THE FASCIiE OF THE PELVIS. 133 



ilio-coccygeal portion of the levator ani to the obturator fascia 

 is the same as that of the muscle. 



What structures are represented in the prominent aponeu- 

 rotic membrane on the side wall of the pelvis, between the 

 attachment of the ilio-coccygeus and the ilio-pectineal line ? 

 Undoubtedly, in some cases, the membrane consists essentially 

 of two layers, more or less fused together. The separation can 

 most easily be effected by dissecting from the perineum, and it is 

 then evident (PI. XIV.) that the ilio-coccygeus is continuous 

 with a thin aponeurosis which, lying on the upper part of the 

 obturator fascia, passes upwards to be attached to the ilio- 

 pectineal line. This confirms the statements of Luschka ^ and 

 Kollmann,- that normally the lateral attachment of the levator 

 ani extends upwards to the pelvic brim. 



Clearly, therefore, there is a somewhat triangular-shaped piece 

 of fascia, above the line of origin of the ilio-coccygeus, extending 

 above as high as the ilio-pectineal line, in front to the back of 

 the pubis, behind to the margin of the great sacro-sciatic notch, 

 the size of which varies, and depends entirely on the level of the 

 tendinous arch of the levator ani. It is not a simple structure, 

 but consists of two layers of fascia of different origin ; one lying 

 on the inner surface of the obturator internus, the other in 

 contact with the peritoneum. After separation, it is clear that 

 the former is continuous with the lower perineal portion of the 

 obturator fascia, and the two constitute the covering for 

 the obturator internus muscle. Of the thin aponeurosis with 

 which the ilio-coccygeus is continuous, I venture to suggest that 

 it represents the upper fibres of the ilio-coccygeus and the 

 investing fasciae. That such a degeneration may occur, and lead 

 to the formation of a tendinous aponeurosis or fascia, is strongly 

 supported by a comparison of the flexor group of tail muscles in 

 the macaque monkey or marmoset, and the orang-utan. The 

 shortening of the tail and the partial assumption of the erect 

 posture in the orang-utan has led to specialisation or divergence 

 from the common or general arrangement which the tailed forms 

 manifest. 



1 Luschka, H., Die Anatomie dcs Menschen, Tubingen, 1864. 

 - Kollmann, J., " Der Coccygeus und der Levator ani bei den geschwanzten 

 Affen und den Anthropoiden,'' Anat. Anz., ix Band, May 1894. 



