INTRODUCTION. 
XIX 
blit, in consequence of the increased size of the posterior molars, the premolars, and 
eventually even the anterior molar, are shed as the posterior molars come into position 
from behind. This animal attained the size of a moderately large Indian Elephant, 
and except for the inflexibility of the mandible-supported trunk must have been very 
similar in appearance. In the later Miocene the mandibular symphysis shortened, 
leaving the trunk mobile and unsupported, as we now know it ; at the same time traces 
of its original elongated condition are retained in the occurrence of deciduous lower 
incisors in some species of and in the peculiar sharp process of the symphysis 
in the Elephants. In the teeth there is a gradual increase in the number and height 
of the ridges composing the molars, together with the great increase in the size of the 
individual teeth. The milk-teeth are never replaced by premolars, but are early 
displaced by the advance of the molars into position from before backwards ; the 
culmination of this line of evolution is met in the latest Elephants, in which in old age 
the only cheek-teeth in position are the very large third upper and lower molars. 
The above is, of course, only a general summary of the succession of forms which 
lead up to the modern Elephants, and no doubt there have been many checks and 
side-branches leading only to extinction in the course of the vast period that has 
elapsed since Moeritheriiim existed. 
The position of Barytherium in relation to the other Ungulates is quite uncertain. 
It cannot be related to Arsinoitherium, since not only are the teeth widely different 
in type, but the anterior part of the dentition, in the mandible at least, has undergone 
great modification, the anterior lower premolars, canines, and posterior incisors having 
been lost and the anterior incisors modified to form large procumbent tusks. In this 
respect it approaches the primitive Proboscidea, but the fore limb so far a§ knoAvn 
differs widely from the Proboscidean type : this is especially noticeable in the distal 
articulation of the radius, which rather resembles that seen in Uintatherium than that 
found in the Elephants, and seems to show that the carpus differed considerably from 
that of the latter group. Another possibility must be referred to, namely, that 
some kind of relationship with the Pyrotheriidae of Patagonia may exist ; in both the 
molars are bilophodont, the anterior lower incisors tusk-like and procumbent and 
separated by a long diastema from the premolars, the other incisors, the canine, and 
anterior incisors being lost ; in the carpus also the scaphoid seems to have been large 
in both groups. The probability of such a relationship Avill be discussed below. 
The Artiodactyla, Avhich are represented in the Upper Eocene by members of the 
Anthracotheriidac and Suidne, may possibly be regarded as a foreign element in this 
