Xv THE TILLODONTIA 507 
These animals have been regarded as ancestral Rodents, to 
which the tooth characters just mentioned clearly show like- 
nesses. The earliest known form is Lsthonyx. This genus shows 
Fic. 247.—Tillotherium fodiens. eft lateral view of skull. (From Flower, 
after Marsh.) 
such primitive characters, compared with its later representatives, 
as the existence of all three pairs of incisors in the upper Jaw, 
but only two in the lower jaw. The enlarged incisors of both 
jaws do not seem to have grown from persistent pulps. 
Anchippodus, a later form, still preserves the upper pair of first 
incisors In a vestigial form; the strong second incisors grew from 
persistent pulps. The most recent genus, 7i/lotheriwm, shows the 
characteristics of the group at their height. The strong Rodent- 
like, chisel-shaped incisors, which are reinforced by a small 
additional pair in the upper jaws only, are persistent. The 
grinding teeth are of the tritubercular pattern; there are three 
of each kind in the upper jaw, but in the lower jaw only two 
premolars on each side. This is at any rate the case with some, 
while others have three. The canine, though present in both jaws, 
is insignificant. As in many ancient types, there is an entepi- 
condylar foramen in the humerus. The feet were five-toed, and 
bore sharp, laterally-compressed claws. The skull has been com- 
pared in general aspect to that of a Bear. 
