284 THE OSTEOLOGY OF ELOTHEEIUM. 



Kowalevsky inferred from the study of his sjjecinien that the foramen ovale " nicht 

 als selbstandiges Foramen existirte, wie z. B. bei den Ruminanten, sondern mit clem For. 

 lac. med. verschmolzen war, wie bei den heutigen Suiden and bei Hippopotamus " ('76, 

 p. 433). This is probably a mistake ; at all events, it is not true of the American 

 species, in which the foramen ovale is a long, conspicuous opening, of oval shape, perfo- 

 rating the alisphenoid. As in the ungulates generally, there is no separate foramen rotun- 

 dum, that opening being fused with the foramen lacerum anterius. The latter is a large 

 and somewhat irregular opening, which notches the anterior border of the alisphenoid, 

 passing between that bone and the orbitosphenoid. The o])tic foramen is small and well 

 separated from the foramen lacerum anterius, lying in front of and at a slightly higher 

 level than the sphenoidal fissure; it does not open so far forward as in E. magnum, and, 

 in consequence, it does not form such a remarkably elongated canal as in the European 

 species (see Kowalevsky, '76, Taf. XVI, Figs. 1 and 3, del), but, on the other hand, it is 

 far from being a simple perforation of the orbitosphenoid, such as occurs in the recent 

 ungulates. This elongation of the optic canal should probably be correlated with the 

 very small size of the brain, which would seem to have been relatively smaller than in 

 the ancestors of the genus. Though the orbits are far behind their primitive jwsition, 

 the backward shifting of the optic tract would seem to have kept jmce with the change in 

 the position of the orbits. 



The posterior palatine foramina are large and conspicuous openings, placed at the 

 maxillo-palatine suture, and separating the two bones at these points; the palatine plates 

 of the maxillaries are deeply grooved for some distance in front of the foramina. The 

 incisive foramina are likewise large, invading both the maxillaries and the premaxilla- 

 ries; indeed, their size prevents the development of any considerable palatine processes 

 on the latter bones. These foramina are in very marked contrast to those of Hippopotcu- 

 mus, in which the enormously expanded and massive preinaxillaries are perforated by 

 two small and widely separated openings; in Stis also the incisive foramina are propor- 

 tionately much smaller than in Elotherivm. The infraorbital foramen is large and is 

 separated from the orbit by a considerable interval, opening above the anterior border of 

 p ^. In front of the foramen a deep groove channels the outer face of the maxillary for 

 a short distance. The canal itself is much elongated, in correspondence with the great 

 length of the jaws, and its posterior orifice, within the orbit, is very large. The lachry- 

 mal foramen, which is single, is quite small and is placed inside of the orbit. 



The supraorbital foramen is subject to some variation in the different species. In 

 E. ingens, from the Titanotherium beds, these openings are of good size, are placed quite 

 near to the median line, and have well-marked vascular channels running forward from 

 them. In specimens of E, mortoni from the Oreodon beds, and in the very large species 



