440 UNGULATA 
The cranial characters exhibit a combination of those found in both 
Perissodactyles and Artiodactyles, but the form of the hinder part 
of the palate and the absence of an alisphenoid canal belong to the 
latter ; and the tympanic, firmly fixed in between the squamosal 
and the exoccipital, ankylosed to both, and forming the floor of a 
long upward-directed meatus auditorius, is so exactly like that of 
the Suina that it is difficult to believe it does not indicate some 
real affinity to that group. These characters seem to outweigh in 
importance those by which some zoologists have linked Toxodon to . 
the Perissodactyla, and the absence of the third trochanter and the 
articulation of the fibula with the calcaneum tell in the same direc- 
tion. According to the recent observations of Ameghino the hind 
feet were certainly tridactylous, and the front feet probably so. 
The earlier allied genera Protorodon and Adinotherium are definitely 
known to have tridactylous front and hind feet, which conform to 
the Perissodactylate type, the bones of the proximal and distal 
rows of the carpus interlocking. Acrotherium, which has similar 
feet, differs from all other Ungulates, and indeed from all Eutherians 
except some individuals of the existing carnivorous genus Otocyon, 
in having eight cheek-teeth, five of which have been reckoned as 
premolars. 
Fic. 192.—Cranium and Lower Jaw of Typotherium eristatum. } natural size. From Gervais. 
Lypotherium. — Typotherium (Fig. 192), also called Mesotherium, 
from the same locality as Tovodon, was an animal rather larger than 
