PAL.^iOMASTODON. 
147 
the condyles {i.c., o.c.) are subcqual, as in E. maxim, us ; tliey are separated by a deej) 
intercondylar fossa, which extends into the inner face of the condyles and is crossed 
obliquely by a ridge running down from the upper inner end of the outer condyle, 
'file trochlear surface is too much broken in this specimen for description. 
A left tibia (PI. XVI. figs. 4, 4 a) from the same locality is, on the whole, like tliat 
of the Elephant. It is, however, rather more slender in the shaft, and the distal 
articulation differs in several important points. At the proximal end the articular 
surfaces are somewhat more obliquely placed than in Elephas, the inner facet (i.) being 
somewhat more elevated with regard to the outer (o.) ; the two facets are of nearly equal 
size. The upper end of the cnemial crest {cn.) is slightly more prominent in proportion 
to the thickness of the shaft than in the Elephant, and both in this and in the other 
points mentioned there seems to be a greater likeness to the tibia of Tetrabelodon. 
On the middle of the front of the shaft there is a vertical groove-like depression for 
the insertion of a muscle. The distal end differs from that of the tibia of Elephas in 
the following points: — (1) the internal malleolus [i.m.) is much more prominent and 
is sharply bounded on its astragalar side by a well-defined groove ; (2) the astragalar 
surface is more strongly concave from before backwards and posteriorly is produced 
downwards into a prominent point near its inner side ; (3) the surface for the fibula is 
smaller and situated further back. The whole surface indicates that the tibial face of 
the astragalus was narrower and more convex from before backwards and interlocked 
much more closely with the tibia than in Elephas ; the broad, gently convex, tibial 
surface of the astragalus in the later Proboscidea not being a primitive character of 
the group. Immediately above the internal malleolus there is on the postero-internal 
face of the shaft a short deep groove, bounded internally by a strong ridge : this is 
wanting in the tibia of Elephas. 
No bones of the foot were found with the limb-bones just described, but a single 
calcaneum (text-fig. 51), from some distance off, so nearly resembles in essential 
characters the calcaneum of the later Proboscideans, more particularly of the Lower 
Miocene Tetrabelodon angustidens, that it may be safely referred to Palceomastodon, 
and from its large size probably belongs to P. beadnelli. 
As might be expected in an animal considerably more lightly built than Elephas., the 
calcaneum is more elongated, the tuber calcis {t.c.) especially being less short and stout. 
In its general proportions this calcaneum more nearly resembles that of Tetrabelodon 
angustidens ; but even in this Lower Miocene form the bone is already considerably 
shorter and stouter. There is a large fibular facet much like that seen in the 
calcaneum of Elephas, except that, instead of narrowing gradually from before 
backwards, it terminates posteriorly abruptly in a nearly vertical border ; it is convex 
from before backwards and looks upwards and outwards. Of the two surfaces for the 
astragalus the ectal (ec.) is the larger ; it is nearly flat, only rising a little towards the 
anterior part of its outer border, where it meets the upper edge of the fibular surface. 
u 2 
