IN VERTEBRATE PALAEONTOLOGY 
111 
animal about as large as the Tapir, which it must have much 
resembled in outward appearance. The molar-teeth have only 
two transverse ridges and the tusks, which are the second pair 
of incisors, were quite small. In the beds above (Upper Eocene) 
is found the next member of the group, Palaeomastodon, the 
species of which range in size from about that of a horse to 
that of a small elephant. In this animal the tusks are much 
larger and the molar teeth have three transverse ridges. The 
anterior part of the lower jaw is greatly elongated, so that it 
projects some distance beyond the skull and must have given 
the animal the appearance of possessing a short stiff 
proboscis. 
Up to this period Proboscidea are known only from Egypt, 
but between the Upper Eocene and the Lower Miocene, the 
next horizon at which they have been found, they had 
spread over much of the world, having passed out of Africa 
along some land connexion with Europe or Asia, which broke 
down the isolation of that part of Africa in which they had 
originated ; the anthropoid apes, Hyraxes, and other members 
of the same fauna, no doubt spread north with them. In the 
lowest Miocene beds of Europe and India the Proboscidea are 
represented by two distinct types. One, Tetrabelodon , is really 
a Palaeomastodon with its peculiarities exaggerated, the hind 
molars having acquired more numerous ridges, the tusks being 
very large and the anterior part of the lower jaw greatly 
elongated. The other form, Dinoiherium (see fig. p. 112), 
is very different and presents peculiarities not found in any 
other of the elephants ; thus the symphysis of the mandible, or 
chin, is turned sharply downwards and bears a pair of large 
recurved tusks. The molar- teeth also remained simple, only 
possessing two transverse ridges (except the first, which has 
three). In fact while Tetrabelodon, by the gradually increasing 
complication of its molars and the shortening up of the 
elongated mandible, leaving behind the flexible proboscis, gave 
rise to the modern elephants, Dinoiherium, although continuing 
to exist till the Pliocene, made no further progress beyond 
_ e increase in size. These two very different types of Proboscidea 
are, as already mentioned, found in company in the Lower 
Miocene beds of Europe and India ; but in deposits of the same 
Vol. II.— No. 4. 
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