MR. ST. G. MIVART ON THE SKELETON OF THE PRIMATES. 205 
forms. In absolute length this segment falls short of that of the Chimpanzee, and it is 
very much shorter than the homologous part in Man and the Gorilla. 
Compared with the length of the spine, that of the tarsus is very slightly less than in 
the Chimpanzee, but falls more short of that in Man and the Gorilla. ‘The proportion 
borne by it to the whole length of the pes is more characteristic, as in the Orang it 
appears to be only as about 26°6 to 100, while in Troglodytes it is 36 or 40 to 100, and 
in Man is as about 46 to 100. 
Calcaneum. (Plate XLIII. figs. 2-7.) 
The os calcis of the Orang is very unlike that of Man, or that of the Gorilla, and 
more resembles that of the Chimpanzee. The projection of the heel backwards 
beyond the hinder margin of the posterior articular surface for the astragalus, some- 
times about equals, sometimes falls short of the antero-posterior extent of that surface. 
The Orang in this differs widely from Man, and still more from the Gorilla, in which 
last the length of the os calcis behind the posterior margin above-mentioned exceeds 
that of all the bone anterior to it. In the Chimpanzee the length of the os calcis 
behind the posterior articular surface for the astragalus does not quite equal the 
antero-posterior extent of that surface, which, again, exceeds that of the bone in 
front of it. 
In the Orang the length of the os calcis anterior to the same surface (Pl. XLIII. 
fig. 6) sometimes equals, sometimes falls short of that of the bone behind it. The 
upper surface of the last-mentioned posterior portion is more or less concave antero- 
posteriorly (Pl. XLIII. figs. 2 & 3), more so than generally in the Gorilla, though 
not so much so as in the Chimpanzee. 
The posterior surface of the tuberosity is more narrow' transversely than in Man 
or Troglodytes, and is prolonged both upwards and downwards, the latter making the 
plantar surface much concave antero-posteriorly (Pl. XLIII. figs. 2, 3, & 5). Although, 
when the surfaces for the astragalus are horizontal, the tuberosity inclines strongly tibiad 
at its plantar end,—yet this inclination is (sometimes at least) not so great as in the 
Gorilla?. The outer or peroneal face of the calcaneum has a somewhat more human 
aspect than has that of the Gorilla, inasmuch as it is vertically less convex and more 
extended, relatively, than in the latter; sometimes even there is a slight vertical 
concavity. 
The posterior articular surface for the astragalus is not so convex as in Troglodytes, 
and it is more posteriorly placed, with respect to the anterior articular surface, than is 
the case in that genus or in Man. As in the Chimpanzee, there is no trace of a second 
posterior plantar tubercle; that for the external lateral ligament is more posterior in 
position than it is in any of the higher forms, though in this the Orang more resembles 
* Professor Huxley remarks, “‘ The calcaneal process is narrow from side to side,” ‘ Medical Times,’ 1864, 
vol. i. p. 565. * Dr. Lucae remarks this, /oc. cit. p. 304. 
