44Q 



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 Protoxodon and Adinothermm 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. 





Fir;. 192.— Cranium and Lower Jaw of Typotherium cristatum. J natural size. From Gervais. 



Typotherium. — Typotherium (Fig. 192), also called Mesotherium, 

 from the same locality as Toxodon, was an animal rather larger than 



