MR. ST. G. MIVART 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 avetabulum, including (as 
before said) the whole of its depressed tract. Below the socket for the femur the 
other part of the antero-external face (Pl. XX XIX. fig. 4) presents (as in 7'roglodytes) 
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 the 
acetabulum from the ischiatic tuberosity. ‘The postero-external surface of this part of 
the ischium (P]. XX XIX. fig. 1) is similarly elongated as compared with Man’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 (Pl. XX XIX. figs. 1-4) than in the Gorilla, and 
sometimes than in the Chimpanzee also, 
The tuberosity of the ischium is formed very much as in Man, and is less flattened 
beneath, and has its margin somewhat less everted than in 7roglodytes. 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 (Pl. XX XIX. 
fig. 6), and less in that of the spine of the ischium than it isin him. It is, however, 
decidedly more prolonged up backwards towards the last-named process, than in 7’rog/o- 
dytes (Pl. XX XIX. tig. 37). 
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 surface is also more concaye, 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 
(Pl. XX XIX. fig. 47°). 
The acetabulum is deepest superiorly, and more predominantly deep there than in 
Man, and somewhat more so than even in Zroglodytes. 
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 
1 Owen, Trans, Zool. Soc, vol. v. p. 14. 
