134 DR PETER THOMPSON. 



In the macaque and marmoset (PI. XV,) the flexor muscles of 

 the tail comprise the pubo-coccygeus, ilio-coccygeus, and sacro- 

 coccygeus, the two former being the morphological equivalent of 

 the levator ani of anthropoid apes and man. The pubo-coccygeus 

 takes orgin from the back of the body of the pubis, the ilio- . 

 coccygeus from the ilio-pectineal line as far back as the sacro-iliac"^ 

 synchondrosis, and both are inserted into the proximal caudal 

 vertebrae. According to Kollmann, the pubo-coccygeus in 

 tailed apes is divisiljle into two parts, a ventral portion arising 

 from the back of the symphysis, and a lateral portion arising 

 from the upper angle of the symphysis as far as the obturator 

 canal, but I failed to find this division in the macaque and 

 marmoset. 



In the orang-utan, the coccygeal vertebrae are represented by 

 two or three rudimentary structures, and the pubo- and ilio- 

 coccygei are remarkably modified to form a muscular diaphragm 

 very similar to what is found in the human subject (PI. XVI.). 

 In the specimen (a well developed female) which I have recently 

 had an opportunity of dissecting, the pubo-coccygeus and ilio- 

 coccygeus were not separable, but fused into one continuous layer. 

 One of the most obvious differences, however, in the muscles, 

 when compared with those in the tailed monkeys, was the reduc- 

 tion of large portions to fibrous aponeurosis. In fact the only 

 part of the layer which was muscular at its origin was the 

 ventral portion of the pubo-coccygeus. The more detailed 

 arrangement of the two muscles is as follows : — 



The ilio-coccygeus appears to arise from the fascia obturatoria 

 along a line extending from the middle of the symphysis pubis 

 to the ischial spine, but this is more apparent than real, since 

 on dissecting the levator ani from the perineum the muscle 

 separates from the pelvic wall almost as high as the ilio-pectineal 

 line, and it is then seen that the upper part of the muscle for 

 lA^ to 2 inches below the origin is remarkably aponeurotic. The 

 posterior fibres are inserted into the sides and tip of the coccy- 

 geal vertebrte, whilst those further forward pass to the middle 

 line, and joining with the corresponding fibres of the opposite 

 side, form the upper part of the muscular sling which is such a 

 prominent feature in the orang-utan. The hinder edge of the 

 ilio-coccygeus is continuous with a well-marked layer of fascia 



