ME. ST. GEOEGE MIYAET ON THE SKELETON OE THE PEIMATES. 
347 
In none is the long axis of the heel, or are the peroneal and tibial surfaces of the 
os calcis so vertical as they are in Man, but the bone is generally twisted, so 
that the sustentaculum tali forms a more or less acute angle with the long axis of 
the tuberosity ; in Man, however, it is a rectangle. This twisting of the os calcis is 
very slight in the Orang and Pithecia, and not great in Ateles and LLylobates. It is more 
marked in the lower Simiidse, and considerably more so still in Troglodytes. Amongst 
the Lemuroidea it is less so in Tarsius, Cheiromys, and Indris than in others, but it 
reaches its maximum in the Nycticebinse, where, in Perodicticus, the sustentaculum tali 
is almost, if not quite parallel with the long axis of the tuberosity. 
Concomitantly with this intwisting, the part answering to the inner face of the 
human calcaneum generally becomes more concave (though scarcely if at all more so in 
the Gorilla than in Man), reaching its maximum in Loris, where the tuberosity bends 
round and meets the posterior margin of the astragalus. 
Again, a narrowing of the part which answers to the plantar surface of Man, also 
accompanies this intwisting. This part, indeed, becomes reduced to a narrow ridge by 
the approximation below of the inner and outer surfaces of the os calcis, and even in the 
Gorilla it is considerably narrower than in Man *. 
The antero-posterior concavity of this plantar surface is very great in Troglodytes, 
being in both species greater than in Manf (Plate XIII. tig. 6), as also in the 
Nycticebinse. On the other hand, in the lower Simiidee and Cebidse, Hapale, Indris, 
and Lemur, this surface is generally almost or quite level antero-posteriorly. 
The length of the tuberosity behind the posterior margin of the posterior articular 
surface for the astragalus, is much longer than that surface in the Gorilla (Plate XIII. 
fig. 6), often so in the lower Simikke, and sometimes in Cebus, very slightly so in 
Perodicticus, and perhaps also in Tarsius J. 
In Man the tuberosity about equals, or rather exceeds the same posterior articular 
surface, but never (except perhaps in some Negroes) equals the predominance attained 
in the Gorilla, where the part behind the posterior surface for the astragalus exceeds 
in length all the bone anterior to the hinder border of that posterior articular surface, 
and in this respect the Gorilla may be said to have the longest heel of any Primate 
(Plate XIII. fig. 6). 
In the Galago the part behind this posterior surface for the astragalus about equals 
in length the antero-posterior dimension of that surface. In forms other than 
those before mentioned, it falls short of it ; in Simia it is only half of it, and in Loris 
even much less than that. 
The length of the heel behind the posterior articular surface for the astragalus 
* But in the Gorilla , as Professor Huxley observes, “ the caleanenm retains its narrowness and the single 
tubercle” (Medical Times, vol. i. p.537). The two plantar tubercles of the plantar surface of the os calcis 
are only found distinct in Man. 
t Its greater concavity is noticed by Professor Owen (Comp. Anat. of Vertebrates, vol. ii. p. 550). 
J See Buemeistee’s ‘ Tarsius,’ pi. 1. 
MDCCCLXV1I. 
O B 
