PYROTHERIUM 161 
The atlas of Pyrotherium is peculiar in having a marked 
hypophysis which is unusual, but is a feature of the atlas 
of Palaeomastodon and Moerithertum. The axis is peculiar 
in that the odontoid is flattened on the upper side and 
very short and wide. In this the form is unique. The 
continuation of the articular surface on the lower side of 
the odontoid with the articular surfaces of the ant. cotyles 
is a feature also of elephants. The remaining cervicals 
are greatly shortened almost to plates, which is elephantine 
again, though this short neck 1s approximated by Dipro- 
todon, some Amblypods and Arsinotherium, so that it 
must be in general looked upon as an adaptive feature, 
though in its detail it shows again an elephant character. 
The upper members of the limbs are longer than the 
lower, which is common to many massive animals. The 
humerus is tremendously flattened from front to back, 
even more so than in any of the animals used for compari- 
son, though flattening is a feature of them and of the 
elephants the most so. With the flattening, the deltoid 
ridge is prolonged enormously making a crest along the 
outer side of the bone, which at the lower end rises in a 
prominent process, as in elephants (also in Diprotodon 
but in this case the rest of the bone is very different). 
In addition to this, the supinator ridge is prolonged up- 
ward until it almost meets the deltoid, ending in a sharp 
spur at the top. This spur is more marked in Pyrotherium 
than in elephants, although they show the same develop- 
ment of the supinator ridge. 
The femur has the head much higher than the greater 
trochanter, which is a feature common to elephants, 
Diprotodon, Arsinotherium, etc., so that it must be looked 
upon as an adaptation. The third trochanter has disap- 
peared, and in elephants, it is lost in the advanced forms, 
remaining however as a trace in Palaeomastodon. 
The tibia is very short and massive and hardly gives 
any suggestions of relationship, except that it is not fused 
It 
