MAMMALIA. 



25 



Pliocene Hipparion. The grinding teeth in these animals Table-case 

 are less deepened than in the last-mentioned genus, those of 5 - 

 the earlier forms being indeed quite low-crowned and only 

 fit for comparatively succulent vegetation. The side-toes 

 tend to become larger and touch the ground as they are 

 traced back in geological time. Typical remains of Anchi- 

 therium (Fig. 13, 3), from the Middle Miocene of Europe, and 

 of Mesohippus, from the Oligocene of North America, are 

 exhibited in Table-case 5. 



The Eocene horse-like animals are still smaller than the Pier-ease 9. 

 later forms just mentioned, and their immediate connection Table-caBe 

 with the horses would be difficult to recognise if all the links 

 of Oligocene and Miocene age remained unknown. A plaster 



Pig. 14. — Left upper teeth in maxilla of Palssotherium crassum, from trie 

 Upper Eocene Gypsum of Montmartre, Paris ; three-quarters nat. size. 

 larSa, three molars ; \p-±p, four premolars ; other letters indicate 

 various tooth-cusps. (After A. Gaudry.) 



cast of Protorohippus venticolus from the Wind Eiver Forma- 

 tion of Wyoming, U.S.A., exhibited in Pier-case 9, affords a 

 good idea of one of these animals about as large as a fox, 

 and there are actual remains of the closely related Hyraco- 

 therium (Fig. 13, 4) from the London Clay (Lower Eocene) 

 of the London Basin in the same Case. The ridges on the 

 grinding teeth are more or less subdivided into tubercles; 

 the neck is not very mobile ; the fore limb has a complete 

 and separate ulna, allowing some power of twisting, and 

 there are four spreading toes ; the hind limb has only three 

 complete toes. Palseotherium, and Lophiodon are allied genera 

 from the Eocene of Europe, and comprise some species as 

 large as rhinoceroses. Palseotherium (Figs. 14, 15) was first 



