THE EVOLUTION OF THE MAMMALIA. 239 
development, and is now the dominant, the most abundant, and 
the most widely spread group of hoofed animals. Its origin is 
still somewhat obscure, but it seems to take its rise from certain 
small animals of the European upper Eocene (genus Dichobune), 
which closely resemble the Bridger ancestor of the camels. This 
supposed beginner of the pecoran series was a short limbed, 
short footed, four-toed animal, with complete dentition and with 
conical tubercles on the grinding surface of the molar teeth. 
From this point onwards, the Pecora pursue a course entirely inde- 
pendent of the camels, but in many and curious ways parallel 
with them. In the Oligocene we find the first genus that can 
be assuredly referred to the Pecora (Gelocus), which is still a very 
small and hornless animal ; the upper canine teeth have become 
scimitar-like tusks, and the cusps of the molars have already 
taken on the crescentic shape, but still retain distinct traces of 
their original conical form. The ulna and fibula are already 
much reduced, as are also the lateral digits of both fore and hind 
foot ; the long bones of these digits are mere threads, interrupted 
in the middle ; the median digits are enlarged, to carry the whole 
weight of the animal, and are beginning to coalesce into a can- 
non bone. In the lower Miocene, the teeth and feet have 
attained nearly their modern stage of development ; the upper 
incisors have all disappeared, and the cannon bones in the feet are 
completely formed. In the middle Miocene appear animals with 
horn-like growths from the skull, which at first are neither 
antlers, like those of the deer, nor true horns, like those of the 
antelopes. From this point, or even earlier, these series diverge ; 
one is that of the hornless deer, which, in the males, retain the 
long, sabre-like upper canine ; the second is that of the true deer, 
which, likewise in the males, have bony antlers, or horn-like 
processes, annually shed and annually renewed, and in which the 
upper canine teeth are much reduced or entirely suppressed. 
The other series leads to the hollow-horned ruminants (Cavicornia), 
in which a pair of bony processes of the skull are covered with 
permanent horny sheaths. Of this series the most ancient and 
the least advanced is the great family of the antelopes, and from 
