HISTORY OF THE fTOXODONTIA 477 



the premolars reduced to two in the upper and one in the lower 

 jaw. The molars were large, persistently growing and thor- 

 oughly hjrpsodont ; in pattern they were very similar to those of 

 \Toxodon. The skull without the lower jaw was low and the 

 cranial portion broad and flattened, but retaining a long sagit- 

 tal crest. The eye-sockets were nearly, but .not quite, closed 

 behind by the very long and slender post-orbital processes of 

 the frontal bones. In front of the eyes the face was suddenly 

 constricted into a long, narrow rostrum, and it is this shape of 

 the skull which, together with the persistently growing, scal- 

 priform incisors, gave such a rodent-like appearance to the 

 head. The auditory region had the same remarkable struc- 

 ture as in the fToxodonta. The lower jaw had a short hori- 

 zontal portion and very high vertical portion, which gave the 

 head great vertical depth. 



The skeleton, so far as it is known, was decidedly more primi- 

 tive than that of the contemporary \Toxodon, as is shown by the 

 presence of collar-bones (clavicles) and by the larger nxmiber 

 of digits, five in the front foot and four in the hind. The hoof- 

 bones, or ungual phalanges, were narrow, pointed and nail-like, 

 though in the hind foot they were broader and more hoof-like. 



Little can be done as yet in tracing back the history of this 

 family, the Santa Cruz beds having yielded no member of it. 

 In the Deseado stage, the genus ^Eutrachytherus differed 

 surprisingly little from \Ty'potherium, in view of the long hiatus 

 in time between them. The Deseado genus already had 

 thoroughly hypsodont and rootless teeth, and the molar pattern 

 was quite the same as in ^Typotherium, but the teeth were much 

 more numerous, the formula being : i ^, c \, p i, m %, X 2 = 42. 

 Nothing is known of the skeleton. The family arose probably 

 from one of the Eocene families (fArchaeopithecidae or fAcce- 

 lodidse) with low-crowned teeth, but the connection cannot be 

 made out. Presumably, the development of this family ran 

 its chief course in some part of South America far to the north 

 of the fossil-beds of Patagonia. 



