612 The Phylogeny of the Camelide. [July, 
gressive remains to be ascertained. In one respect this line ex- 
hibits a high specialization, which is present at the earliest known 
period of its history. This consists in the reduction of the lat- 
eral (11 and v) metapodial bones, so that but two functional toes 
remain (see Fig. 1, c-/). This condition has been reached by 
the more typical artiodactyles after a much longer lapse of time, 
for most of the extinct and recent types display lateral digits ina 
well-developed or rudimentary condition; in but few of them 
have they totally disappeared. In another respect the line of the 
= — Camels attains a higher specialization than that of the typical 
ruminants, although its beginning is that which is common to the 
entire suborder. This is in the dentition. The reduction in 
numbers of teeth showed by Owen to characterize the historical 
succession of all Mammalia, is carried further in the molar series 
of camels than in any hoofed order; for in the final term or 
| genus, Eschatius (Cope), there is but one premolar left in the 
| upper jaw, and that is reduced to a simple cone. The true 
molars never reach the complexity of those of the other line, of 
` the Bovidz or oxen, nor do they become prismatic as in that 
family, but retain the short crown well distinguished from long 
roots, which belongs to all the earlier Mammalia. 
ae The successional reduction in the numbers of premolar torth 
ko in the family of the Camelide is shown in the following table. 
__. There is seen in the genera Protauchenia and Palauchenia a ten- 
dency to an increase of complication of the fourth inferior pre- 
molar, j 
I. Premolar teeth 4, a 
1847. 
P-m. 1 separated by diastema - -- Procamelus Leidy 
~> < IL Premolar teeth 4. ‘ ; 
o Pien below wanting vee. Pliauchema s5 
III. Premolar teeth 3. 
’ Linn, 
_ Fourth inferior premolar IRN OMISE oi ER E S SE e Sm ine 
_ Fourth inferior premolar composed of two crescents, which enclose a lake ( Owen. 
ve a iiaa Palash Oe ~ d 
Ie Be 1 . ior tul 
Fourth inferior premolar composed of two crescents, with two posterior 
s ind them., otauchenia 
a Y. Premolar teeth 3. 
Fourth premolar below Wane er ors do eck. sc he ows ose tee eke 
V. Premolar teeth 4. 
Cope. 
oath superior premolar consisting of a simple cone.....+e+-+*** pgs 
Fourth superior premolar composed of two crescents.....+- ro ee Cope. 
ete 
