32(3 PALAEONTOLOGY 



determine the hoofed nature of this species, and its affinities 

 to the Perissodactyla, or the order of Ungulata with toes in odd 

 number. The extent and well-defined boundary of the tem- 

 poral fossae by the occipital (3), parietal (7), and post-frontal 

 ridges, and their free communication with the orbits, give 

 almost a carnivorous character to this part of the cranium of 

 Pliolophus ; but as in the hog, Hyrax, and Palieothere, the 

 greatest cerebral expansion is at the middle and toward the 

 fore part of the fossae, with a contraction toward the occiput ; 

 the brain-case not continuing to enlarge backward to beyond 

 the origin of the zygomata, as in the fox. The zygomatic 

 arches have a less outward span than in the Camivora. In 

 this part of the cranial structure Pliolophus resembles Palceo- 

 therium more than it does any existing Mammal ; but the 

 post-frontal processes are longer and more inclined backward. 

 The incompleteness of the orbit occurs in both Anoplotherium 

 and Palceotherium, as in Rhinoceros, Tapirus, and the hog tribe ; 

 but in the extent of the deficient rim, Pliolophus is inter- 

 mediate between Palceotherium and Tapirus. The orbit is not 

 so low placed as in Palceotherium, Tapirus, and Rhinoceros, 

 nor so high as in Hyrax or Sus. The straight upper contour 

 of the skull ( 7 to 15) is like that in the horse tribe and Hyrax, 

 and differs from the convex contour of the same part in the 

 Anoplothere and PaLTothere. The size of the antorbital fora- 

 men («) indicates no unusual development of the muzzle or 

 upper lip. In the conformation of the nasal aperture by four 

 bones (two nasals, 15, and two premaxillaries, iz), Pliolophus 

 resembles the horse, Hyrax, hog tribe, and Anoplothere, and 

 differs from the rhinoceros, tapir, and Pala?othere, which have 

 the maxillaries, as well as the nasals and premaxillaries, enter- 

 ing into the formation of the external bony nostril. 



The ungulate and herbivorous character of Pliolophus is 

 most distinctly marked by the modifications of the lower jaw, 

 especially by the relative dimensions "I the parts of the ascend- 



