INTliODUCTIOX. 
X\ 11 
The limbs are unfortimately not well known. The humerus ditfers considerably from 
that of the later Proboscidca, but some of tlie smaller species of Paloeomadodon (see 
text-fig. 50) from the Ujiper Eocene seem to supjily intermediate forms: probably 
the difference arises from the fact that Mceritlteriimi 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, Maeritherium was probably an amphibious, shore, or swam]) 
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 Proboscidca : to this creature the name Palceomastodon has been given. 
The intermediate links between it and Mceritherium or some allied form are not yet 
definitely known, unless some of the smaller species referred to Palceomastodon, under 
the names P, minor Kndi P. jjarvus, or the animal called M. trigonodon, oxe 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 Mceritherium lyonsi and Pal oeo mastodon 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 fleshy 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 Mceritherium, 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 
