1G6 
TEETIARY VERTEBRATA OF THE FATCM. 
is the larger and is widest from before backwards ; at its antero-external angle it runs up 
on to the prominent intercondylar process (ic.p.), on the outer side of which there is a 
dee]) fossa for the atiachment of ligament. The outer facet (o.) is widest from side to 
side, and beneath its outer edge there is a flattened surface, apparently for the u])per end 
of the fibula. The upper part of the not very prominent cnemial crest {cn.) is divided 
into two by a deep depression, the outer portion being the largest. The middle portion 
of the shaft is flattened behind and convex in front; towards the distal articulation it 
widens out and hears on its postero-internal surface a prominence (p.) forming the outer 
siile of a groove, ])recisely similar to that seen in the tibia of P. headnelli. The distal 
articulation is also like that found in the large species : there is a prominent internal 
malleolus {i.m.) bearing an astragalar facet looking outwards and forwards ; external to 
Text-fig. 57. 
Right ulna of Palcfomastodon parvus: A, from front; B, from inner side. 
oJ., olecranon process ; rp., radial groove ; r.s., radial surface, j nat. size. 
this is the main surface for the astragalus strongly concave from before backward.'), 
and is })roduccd downwards into a blunt point both before and behind. External to this 
surface there is a roughened facet (/.) looking downwards and outwards, a})j>arently for 
articulation with the tibula. The chief difference between this tibia and that of PUphas 
is in the form of the distal articulation. In tlu' recent form, probably owing to tlu' 
increasing size and weight, the astragalar surface is much broader and more gently 
concave, and this increase of width has led to the reduction of the internal malleolus to 
a mere blunt ])oiut. Otherwise the two tibias are very similar even in small ])oints. 
