INTEODUCTIOlSr. xvu 



The limbs are unfortunately not well known. The humerus differs considerably from 

 that of the later Proboscidea, but some of the smaller species of Palceomastodon (see 

 text-fig. 56) from the Upper Eocene seem to supply intermediate forms : probably 

 the difference arises from the fact that Moeritherium was a more or less amphibious 

 type, while the later Elephants became fitted for progression on firm ground. The 

 femur approximates very nearly to the form found in the later Proboscideans. 



As already mentioned, Moeritherium was probably an amphibious, shore, or swamp 

 living animal, and it was no doubt owing to the continuation of the conditions 

 favourable to its mode of life that it persisted into the Upper Eocene period. In the 

 meantime, however, either from this or some closely allied type, there had arisen another 

 animal more adapted to terrestrial life and showing a great advance in the direction 

 of the typical Proboscidea : to this creature the name Palceomastodon has been given. 

 The intermediate links between it and Moeritherium or some allied form are not yet 

 definitely known, unless some of the smaller species referred to Palceomastodon, under 

 the names P. minor and P. parvus, or the animal called M. trigonodon, are such. 

 Certainly in many respects the limb-bones, particularly the humerus (see text-fig. 56, 

 p. 164), referred to P. parvus, are both in size and structure intermediate between 

 those of Moeritherium lyonsi and Palceomastodon headnelli. 



The largest species of Palceomastodon (P. headnelli) must have been about the size 

 of a half-grown Indian Elephant : in its general appearance it was Elephant-like, but 

 differed in having a longer neck and the symphysial portion of the mandible prolonged 

 beyond the skull (see text-fig. 48, p. 131) and covered only with the fieshy snout. 

 Probably it could reach the ground with its lower incisors, and the end of the snout 

 may already have been prehensile. In the skull the chief peculiarities are : (1) the 

 external nares are shifted backwards, so that they are only just in front of the 

 orbit, and, in consequence, the nasal bones are shortened and relatively very small ; 

 (2) the back of the skull is greatly enlarged by the development of spongy bone in the 

 occipital region. The occipital surface above the prominent condyles slopes a little 

 forwards and has a deep median fossa for the attachment of muscles. The upper 

 dentition is much more reduced than in Moeritherium, and now assumes more 

 definitely Proboscidean characters. The only remaining incisors are the large tusk- 

 like second pair, which are directed downwards and have a band of enamel on their 

 outer side. Sections of these tusks examined microscopically show no traces of the 

 peculiar " engine-turning " so characteristic of the dentine of the tusks of the later forms. 

 Either this structure was only acquired when the tusks became greatly enlarged or the 



