322 SCOTT. [Vol. XI. 



developed. From the upper margin of the maxillaries arise 

 the most anterior and the largest of the protuberances. " The 

 whole conformation of the maxillaries is, so far as we know, 

 unique among the mammalia ; the superior borders curve 

 sharply upward into two powerful plates of bone, concave on 

 the outer side, convex on the inner, and rising to the level of 

 the parietal processes, with a concave posterior and convex 

 anterior border" (Osborn and Wortman, No. 8, p. 357). The 

 concavity of the outer surface is interrupted by two convex 

 ridges, one of which is the continuation upward and forward 

 of the masseteric ridge, though its smooth surface shows that 

 it is not a part of that ridge, and the other is the bulging 

 caused by the alveolus of the large canine. These maxillary 

 protuberances are, as we have already seen, shown in the 

 female skull by a slight upward arching of the borders of the 

 maxillaries ; in some specimens they are quite distinct, and 

 have slightly thickened and rugose margins, though not in any 

 degree approximating their great size in the male. In Uinta- 

 tJiei'iiini the maxillary protuberances are rounded and horn-like, 

 while in Protoceras they are plates. Sus larvatus, a recent 

 species from Africa, has maxillary protuberances which are 

 thick and very rugose. The infraorbital foramen is slightly 

 more anterior in position in the male, and in that sex the pre- 

 maxillary spines are rather narrower, so that the incisive fora- 

 mina are somewhat more widely open. All the bones of the 

 skull are thicker and more massive, as a result of which the 

 male skulls are seldom so distorted by pressure as the female 

 specimens very generally are. 



Still a third kind of skull-structure is presented by the type 

 specimen of Protoceras celer, as described and figured by 

 Marsh (Nos. 5, 6). This specimen is imperfect and some 

 points of importance cannot be determined from it. On the 

 whole, it agrees best with the females which have already been 

 described, but in none of the latter which I have seen are the 

 parietal protuberances anything more than mere roughenings 

 of the temporal crests, while in the type specimen they are 

 fairly well developed, conical eminences, which are described 

 as " a pair of small horn-cores, situated not on the frontals. 



