FOSSIL VERTEBRATES— MAMMALIA $31 
There are generally recognized eight suborders of this order: 
Condylarthra. 
Pertssodactyla. 
Artiodactyla. 
Amblypoda. 
Proboscidea. 
LToxodontia. 
Lypotheria. 
yracoidea. 
The Condylarthra are forms with five functional digits on each 
foot ; plantigrade in the habit of walking, and with small hoofs 
oneach digit. The astragulus has a long neck, and the distal 
ankicilan tace. ton tre navicular 1s) rounded: lhe, teeth are 
multitubercular and complete in number in each jaw. It was in 
these regions that the changes took place that have made it pos- 
sible to trace out the lines of development of the ungulates, 
and, as Cope thought, the lines of the Carnivora and the Pr- 
mates as well. 
There are several families of the suborder, but it will be as 
well, probably, to take one of the forms from one of the families 
and describe it as typical of the whole group. 
Phenacodus is the best known of the suborder. By great 
good fortune the nearly perfect skeletons of two individuals are 
known. The whole animal was about the size of a mastiff dog. 
The first and fifth toes on both the fore and the hind feet are 
shorter than the others, and show already the tendency to a 
reduction in number that is the dominant line of evolution in 
the foot structure of the ungulates. Another thing, the bones 
of the two rows of the carpus and the tarsus are arranged one 
above the other, instead of being alternate in position, 2. ¢., one 
of the upper row being opposite the space between two of the 
lower row. The latter arrangement is readily seen to be by far 
the strongest, and the development of the ungulates is marked 
by the gradual acquisition of this alternate arrangement of the 
bones in place of the serial arrangement of the Condylarthra. 
There was a long tail; the skull was low and flat, with large 
