MR. ST. G. MIVART ON THE SKELETON OF THE PRIMATES. 205 
The articular surface for the lower part of the fibula is much larger than in Man and 
Troglodytes, being about the same size as the malleolar one for the inner side of the 
astragalus (Pl. XLI. figs. 5 & 9s). 
The shaft of the tibia is, as in the higher forms, triangular above its middle; but 
below that it is, as in 7’roglodytes, much more rounded than in Man. 
The internal surface is convex, except at its upper part and just within the crest and 
below the tubercle, in which last situation there is, as also in Zroglodytes', a rough 
and depressed surface (Pl. XLI. fig. 1) for the insertion of the sartorius, gracilis, and 
semitendinosus muscles. 
The external, or peroneal, surface of the tibia is, as in 7roglodytes, more strongly 
concave above than in Man, while from rather above the middle of the bone, it merges 
insensibly into the anterior surface. ‘This external surface of the human tibia is much 
broader from behind forwards than is the part which corresponds to it in Simia, if the 
faint ridge (Pl. XLI. fig. 57) running downwards from the front of the upper surface 
for the fibula is that to which the interosseous ligament is attached. 
The posterior surface of the tibia presents an oblique popliteal ridge, which, however, 
as also in 7’roglodytes, is much less strongly marked than in Man. 
The medullary foramen (Pl. XLI. fig. 2”) is much as in Man and the Chimpanzee, 
and more above the middle of the bone than I have observed it to be in the Gorilla. 
The anterior border, or crest of the tibia, is less sharp, much shorter, and inclines 
more markedly tibiad below than in Man, agreeing in these points with Z’roglodytes, 
except that in Sima the crest is rather more sharp towards its upper end. 
The inner border, as also in 7'roglodytes, is so little marked as to be hardly distin- 
guishable, except for a short distance above the posterior border of the malleolus. 
There is a well-marked external or peroneal border, which, however, does not 
correspond with the external border of the tibia of Man, inasmuch as it descends from 
behind, and not from in front of, the upper facet for the fibula; it becomes lost about 
halfway down the tibia. 
Another and less marked external ridge (Pl. XLI. fig. 57) appears to correspond with 
the external margin in Man. It springs from a point anterior to the upper articular 
surface for the fibula, and descends to the apex of the lower articular surface for that 
bone. This ridge is rather more strongly marked in T’roglodytes. 
Fibula. (Plate XLI. figs. 1, 3, 6, 7, 10, & 11.) 
As in Troglodytes®, this bone is much more distant from the shaft of the tibia than in 
Man; it is also shorter, stouter, and straighter than in him, and has the ridges and 
depressions on its surface less marked,—in all which points the fibula of the Orang 
agrees with that of the Gorilla and that of the Chimpanzee. 
The proximal articular surface (Pl. XLI. figs. 7 & 10) is more rounded than in 
' Owen, Trans. Zool. Soc. vol. v. p. 19. * Owen, loc. cit. vol. i. p. 366. 
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