•34 
TKirriAKV VEHTKI51tATA OF THE FAYCM. 
a sli(']f-like ])rqiecti()n !)eariiif>; on its ni])])cr surface a facet (t.) for articulation 
uitli tlie libnlar facet of the tibia above described. 14eueatli this facet tlie distal 
portion of the fibula forming- the external malleolus projects considerably, and its outer 
face is swollen and ronghcned, while its inner, nearly triangular surface bears two 
facets almost iu the same ])lane. Of these facets the u])per (ast.) is the smaller and 
articulates with the astragalus, so that when the tibia and fibula are iu their natural 
position with regard to one another the astragalar facets of the two bones form a 
continuous concave surfirce. The lower and larger facet {calc.) articulates with the 
large fibular facet of the calcaneum, which 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, particularly its distal portion, is extremely like that of Eleplias. In 
both tliere 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 
surfoces for the astragalus and calcaneum. The fibula of TJintafherhmi is different 
in all these particulars, more especially in the very small size or even complete 
absence of the calcaneal facet ; it should, however, be remarked that in the earlier 
Amblypoda, e. g. Conjphodon, the calcaneal articulation of the fibula is well 
developed, and this is no doubt a primitive feature. 
Examples of the astragalus (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 
Arsmoitherium on the followdng 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 tlie possibility of this 
type of astragalus belonging to PaUmmastodon, of which, moreover, the calcaneum 
and probably the astragalus are known. 
From these considerations it w'ill be seen that the astragalus now described may 
be regarded with confidence as that of Arsiuoitherium. The ])roximal articulation 
for the tibia (text-hg. 32, tih.) is gently convex from before backwards, and very 
slightly concave from side to side. Posteriorly there is a notch [n.), but there is 
no perforation as in some of the Dinocerata. The articulation does not extend 
farther back on the inner than on the outer side. On the outer side is the fibular 
surface {fid.) looking outwards and somewhat upwards, and passing above into the 
tibial surface. 
On the inner side the main tibial surfice is continuous with an inner face looking 
inwards and upwards, and sn])])lying a surface for the articulation of the internal 
malleolar process of the tibia. Eeneath and behind this surface the ])ostero-internal 
angle of the bone forms a })rominent tuberosity. The surfaces for the calcaneum 
