136 DR PETER THOMPSON. 



the upper thin aponeurotic origin of the ilio-coccygeus, is thus 

 supported by a comparison with a type closely allied to man, and 

 in which the obturator muscle and its fascia do not reach as 

 high as the ilio-pectineal line.^ In the orang-utan there can be 

 no doubt that the fascia lying on the bone above the apparent 

 origin of the pelvic diaphragm, and seen immediately after 

 removing the peritoneum and sub-peritoneal fat, represents the 

 upper degenerated part of the ilio-coccygeus, a muscle attaining 

 a high state of development in tailed monkeys. 



There now remains to be described the second set of fasciae, 

 which act as fixing or supporting structures to the pelvic 

 viscera. 



In animals in which the long axis of the body is horizontal, 

 the pelvic viscera derive support in a somewhat different way 

 from that obtaining in those in which the axis is either 

 absolutely or approximately vertical. In the former, the 

 viscera are supported by the bony floor of the pelvis (symphysis 

 pubis), whilst the rectum is also suspended from the sacrum 

 and the proximal caudal vertebne. The external sphincter ani, 

 attached to the caudal vertebr£e, forms a sling for the lower 

 end of the rectum, the ilio- and pubo-coccygei passing to their 

 insertion into the tail give support to the lateral parts of the 

 gut a little further forwards, and in carnivores at least special 

 muscles apparently suspensory in function extend from the 

 caudal vertebrae into the walls of the rectum and vagina. 



The assumption of the erect posture — as in man, and ap- 

 proximately so in anthropoids — necessitates special ' modifi- 

 cations for the support of the pelvic viscera. Of these, 

 perhaps the most important are the modifications which the 



^ Very few embryological observations on tlie levator ani liave been pub- 

 lished, but in a recent paper by J. S. Popowski of Tomsk on the development 

 of the perineal muscles in human embryos, reference is made to the way in 

 which the muscle appears. In embryos of 4-5 months the levator ani is incom- 

 pletely formed, being represented by that part which springs from the fascia on 

 the lateral wall of the true pelvis (ilio-coccygeus), and is uninterruptedly con- 

 tinuous with the coccygeus. In six months embryos the levator ani is completed 

 by the development of the pubo-coccygeus. No reference is made to the level on 

 the lateral pelvic wall at which the ilio-coccygeus takes origin. (Popowski, 

 J.S., " iJber die Entwickelung der Muskulatur des Perineums beim menschlichen 

 Embryo." Ernehnhm dcr Anntrymir u. EntxoickeliiiKjsgeschichtc. Merkel und 

 Bonnet, "Wiesbaden, vol. vii., 1898.) 



