54 
TKRTIAIIY YEliTEP/lUTA OF THE FAYCiM. 
a sliclf-liko i)Tojecti()ii l)cnriit^- on its iii)])cr surface a facet (t.) for articulation 
witli tlie tihular facet of tlie tibia, above described. Beneath this facet the distal 
])ortion ()f the til)ula, forniiiif>' tlie external malleolus projects considerably, and its outer 
face is su'ollen and roui>li('ned, while its inner, nearly triangular surface bears Ovo 
facets almost in the same ])lane. Of these facets the upper (ast.) is the smaller and 
articnlates with the astragalus, so that when the tibia and fibula are in their iratural 
position with regard to one another the astragalar facets of the twm bones form a 
continuous concave surface. The lower and larger facet {calc.) articulates with the 
large fibular facet of the calcaneum, wdiich lies immediately external to the ectal facet 
for the astragalus. The astragalar and calcaneal facets of the fibula are only separated 
by a slight ridge. 
The fibula, ])articularly its distal portion, is extremely like that of Elcphas. In 
both there is the same concavity of the inner face of the distal end, the prominent 
facet for articulation 'with the tibia, and an almost identical arrangement of the 
surfaces for the astragalus and calcaneum. The fibula of Uintatherium is different 
in all these particidars, more especially in the very small size or oven complete 
absence of the calcaneal facet ; it should, howmver, be remarked that in the earlier 
Amblypoda, e. g. Con/phodon, the calcaneal articulation of the fibula is well 
developed, and this is no doubt a primitive feature. 
Examples of the a.'drafjahts (text-fig. 32, 2 a, 2 b, 2 c) are among the most numerous 
of the bones found in these deposits, and it is remarkable that of the very large 
number collected nearly all are of the form now described and referred to 
Arshwithcrium on tlie following grounds : — (1) their large size and massive 
structure; (2) the agreement of their articular surfaces with those of the tibia 
above described and with the most common form of calcaneum ; (3) the presence 
of articular surfaces for both cuboid and navicular excluding the possibility of this 
type of astragalus belonging to Fakco mastodon, of which, moreover, tlie calcaneum 
and probably the astragalus are known. 
From these considerations it will be seen that the astragalus now described may 
be regarded with confidence as that of Arsinoithenani. 'J'he proximal articulation 
for the tibia (text-fig. 32, tih.) is gently convex from before backwards, and very 
slightly concave from side to side. Posteriorly there is a notch (w.), but there is 
no perforation as in some of the Dinocerata. The articulation does not extend 
farther back on the inner than on tlie outer side. On the outer side is the fibular 
surface {fib.) looking outwards and somewhat upwards, and passing above into the 
tibial surface. 
On the inner side the main tibial surface is continuous with an inner hree looking- 
inwards and upwards, and snpjilying a surface for the articulation of the internal 
malleolar jirocess of the tibia. Beneath and behind this surface the jiostero-internal 
angle of the bone forms a jirominent tuberosity. 4'he surfaces for the calcaneum 
