of the cervical vertebre (Fig. 1). 
1886.] The Phylogeny of Camelide. 617 
The following suggestions as to the origin of the three pecu- 
liarities of the cameloid series, or Tylopoda as they have been 
called, may be made. The imperfection of the distal metapodial 
keels (Figs. 2, 3 and 7) is probably due to the £} 
early development of an elastic pad of connec- į i 
tive tissue beneath the proximal phalanges. It 
is this pad which gives the foot of the camel its 
peculiar lateral expansion, and causes its step to 
be both elastic and silent. This structure has 
relieved the metapodials of the concussions to 
which the feet of other Ruminantia are subject, 
and I have advanced this fact as the cause of the 
peculiarity of the metapodials above mentioned.? 
The cause of the absence of superior incisor 
teeth is unknown, but has been supposed to be 
complementary to the presence of horns in the 
Ruminantia. None of the camel line have horns, 
and the presence of the single incisor on each 
side may be connected with this fact; but why 
two of the incisors on each side should have 
been lost under the circumstances, is not ex- 
Plained. Nor has any explanation been offered 
for the absence of the vertebrarterial foramina 
: There have been six species of the Pantoles- y 
tidæ described, all belonging to the genus Panto- y y 
a The only ones of the six which are Paq. — Misi 
n from parts of the skeleton, are the P. foot of Počbrotheri- 
“gicaudus Cope, of the Bridger Eocene epoch, = — from 
and the P, brachystomus of the Wasatch Eocene ed in Fig. 1. Orig- 
(Fig. 8). Neither of these species exceeded an e a Wits 
existing musk-deer in size, and both had slender Colorado, 
limbs. The tarsus of the P. érachystomus is known, and it is truly 
ruminant, though all the bones are distinct (Fig. 8). At the upper 
end the adjacent sides of the metatarsal bones are flattened and 
applied together, so that the later formation of a cannon bone by 
their fusion, must have been of easy accomplishment. The dis- 
: tal parts of these bones as seen in the P. longicaudus are not 
closely appressed, but are quite distinct from each other. The P. 
“AMERICAN NATURALIST. 
