PYROTHERIUM l6l 



The atlas of Pyrotheriiim is peculiar in having a marked 

 hypophysis which is unusual, but is a feature of the atlas 

 of Palaeomastodon and Moeritherium. 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 is approximated by Dipro- 

 tvdon, 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 Diprolodon 

 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 Pyrotheriiim 

 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 



