li PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
bone. The navicular and the cuboid unite, and the distal end of the 
fibula is anchylosed with the tibia. 
In Cainotherium and Dichobune the upper incisors are fully deye- 
loped. There are seven grinders; the teeth form a continuous series 
without a diastema. The metatarsals, the navicular and cuboid, and 
the distal end of the fibula remain free. In the Cainotherium, also, the 
second metacarpal, is developed, but is much shorter than the third, 
while the fifth is absent or rudimentary. In this respect it resembles 
Anoplotherium secundarium. This circumstance, and the peculiar 
pattern of the upper molars in Cainotheriwm, lead me to hesitate in 
considering it as the actual ancestor of the modern Tragulide. If 
Dichobune has a four-toed fore foot (though I am inclined to suspect 
it resembles Cainotherium) it will be a better representative of the 
oldest forms of the Traguline series; but Dichobune occurs in the 
Middle Eocene and is, in fact, the oldest known artiodactyle mammal. 
Where, then, must we look for its five-toed ancestor ? 
If we follow down other lines of recent and tertiary Ungulata, the 
same question presents itself. The Pigs are traceable back through 
the Miocene epoch to the Upper Eocene, where they appear in the 
two well-marked forms of Hyopotamus and Cheropotamus; but 
Hyopotamus appears to have had only two toes. 
Again, all the great groups of the Ruminants, the Bouvide, Anti- 
lopide, Camelopardulide, and Cervide, are represented in the 
Miocene epoch, and so are the Camels. The Upper-Eocene Anoplo- 
thervum, which is intercalary between the Pigs and the Tragulide, 
has only two or, at most, three toes. Among the scanty mammals 
of the Lower Eocene formation we have the perissodactyle Ungulata 
represented by Coryphodon, Hyracotherium, and Pholophus. Sup- 
pose for a moment, for the sake of following out the argument, that 
Pliolophus represents the primary stock of the Perissodactyles, and 
Dichobune that of the Artiodactyles (though I am far from saying 
that such is the case), then we find in the earliest fauna of the 
Eocene epoch to which our investigations carry us the two divisions 
of the Ungulata completely differentiated, and no trace of any 
common stock of both or five-toed predecessors to either. With the 
case of the Horses before us, justifying a belief in the production of 
new animal forms by modification of old ones, I see no escape from 
the necessity of seeking for these ancestors of the Ungulata beyond 
the limits of the Tertiary formations. 
I could as soon admit special creation, at once, as suppose that the 
Perissodactyles and Artiodactyles had no five-toed ancestors. And 
when we consider how large a portion of the Tertiary period elapsed 
before Anchitherium was conyerted into Equus, it is difficult to 
escape the conclusion that a large proportion of time anterior to the 
Tertiary must have been expended in converting the common stock 
of the Ungulata into Perissodactyles and Artiodactyles. 
The same moral is inculcated by the study of every other order 
of Tertiary monodelphous Mammalia. Lach of these orders is repre- 
sented in the Miocene epoch: the Eocene formation, as I have 
already said, contains Chiroptera, Insectivora, Rodentia, Ungulata, 
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