210 LEIDY'S OSTEOLOGY OF THE HEAD OF HIPPOPOTAMUS. 



several inches greater, and the breadth, at the posterior part of the zygomatic arch, 

 and at the canine alveoli is also greater, but is less at the anterior part of the arch, 

 just mentioned, and at the infra-orbitar foramen. From the relative sizes stated, the 

 zygomatic arch is of course more parallel in the female, or more convergent to the 

 face, in the male. In the latter a sagittal crest exists, which is three and a half inches 

 long, from the notch at the inion to its bifurcation forwards, in which direction it is 

 descending. In the female there is no parietal crest formed by the conjunction of 

 the temporal ridges, but a broad obtuse ridge presents itself at the summit of the 

 occiput, which trifurcates an inch and a half in advance of the inion ; the lateral 

 portions constituting the bounding temporal ridges ; the middle, a slight rough 

 ridge, an inch and a half long. The middle parietal ridge also in the female, does 

 not descend to the forehead, but is nearly on a level with it. 



The orbits are very much more elevated in the male than the female, and conse- 

 quently the transverse concavity of the forehead is much deeper in the former than 

 in the latter, while its breadth remains nearly the same in both. 



The orbital entrance, and the malar surface below, are directed more upward in 

 the female, and the concavity of the face, just in advance of the former, is less than 

 in the male. 



The ossa nasi are shorter, but considerably broader in the female, and the boss of 

 the canine alveoli is very much shorter, and the concavity of the face, internal to it, 

 correspondingly shallow. 



The orifice of the nose is broader, but a little lower, in the female than the 

 male. 



We have no means of comparing the lower jaw of the male with that of the 

 female. 



The superior incisors and canines are smaller and less exserted in the latter than 

 the former. Their exact form is probably not only variable in the different sexes, 

 but also, to a slight extent, in different individuals, as indicated by the lateral incisors 

 in the two adult specimens of the lower jaw of the male; being very much more 

 compressed laterally in that preserved with the skull, than in the other. 



In the male the superior mid incisors are very slightly bent in their course, are 

 cylindroid, a little compressed antero-posteriorly, six and a half inches long by four 

 inches in circumference, and are protected by a band of enamel, ten lines wide, upon 

 their outer side. The exserted portion is two and a half inches long, projects down- 

 ward and forwards. Its abraded surface is oblique, presents inwards, and is two and 

 a half inches long by one inch broad. 



In the female the protruding portion of the upper mid incisors is three-fourths of an 

 inch long by three and a quarter inches in circumference, is directed downwards and 



