IIE. ST. G. inVAET ON THE SKELETON OF THE PRIMATES. 197 



The ischium consists, as in Man, of a body and ramus; and part of the external 

 surface of the former constitutes the greater portion of the acetabulum, including (as 

 before said) the whole of its depressed tract. Below the socket for the femur the 

 other part of the antero-extemal face (PI. XXXIX. fig. 4) presents (as in TrogJodijtes) 

 a wide surface of bone^concave from above downwards, and strongly convex from 

 behind forwards — in the place of the narrow groove which in Man separates tlie 

 acetabulum from the ischiatic tuberosity. The postero-extemal surface of this part of 

 the ischium (PI. XXXIX. fig. 1) is similarly elongated as compared with ISIan's structure, 

 but in all the forms it is smooth and bounded inferiorly (as is also the outer surface) by 

 the margin of the tuberosity of the ischium. In the Orang this surface is not prolonged 

 backwards, as in Man, by so prominent an ischiatic spine, though this process is 

 considerably more developed (PI. XXXIX. figs. 1-4 h) than in the Gorilla, and 

 sometimes than in the Chimpanzee also. 



The tuberosity of the ischium is formed very miich as in Man, and is less flattened 

 beneath, and has its margin somewhat less everted than in Troglodytes. At the same 

 time the Orang resembles the last-named genus, and differs from Man in that the 

 rugose surface is prolonged more in the direction of the symphysis pubis (PI. XXXIX. 

 fig. 6), and less in that of the spine of the ischium than it is in him. It is, however, 

 decidedly more prolonged up backwards towards the last-named process, than in Troglo- 

 dytes (PI. XXXIX. fig. 3 I). 



The ramus of the ischium in the Orang agrees with that of the Gorilla and that of 

 the Chimpanzee in being very much more vertically extended than in Man. Its 

 external sui'face is also more concave, and its inferior border more everted, while the 

 margin bounding the obturator foramen is thinner than in him. 



The last-mentioned foramen is generally somewhat subtriangular, with one angle 

 turned towards the outer end of the horizontal ramus of the pubis. 



The acetabulum is longer vertically, in comparison with its breadth, than in Man. Its 

 depressed surface and the cotyloid notch are very much smaller than in the higher forms 

 (PI. XXXIX. fig. 4/). 



The acetabulum is deepest superiorly, and more predominantly deep there than in 

 Man, and somewhat more so than even in Troglodytes. 



The anterior part of the pelvis does not descend so much as in the last-mentioned 

 genus, but is more like that of Man in this respect. 



The false pelvis is longer and more shallow than in the Gorilla, and still more 

 so than in Man. As in Troglodytes the inlet of the true pelvis is "less' con- 

 stricted anteriorly, less cordate, and more fully elliptical in shape " than in the 

 human form. The ellipse, however, is, sometimes at least, less elongated than in 

 Troglodytes. 



As in the Gorilla and Chimpanzee, but a small part of the acetabulum is visible 



' Owen, Trans. Zool. Soc. vol. v. p. 14. 



