MAMMALIA. 35 



Miocene formations, with deeper and more effective cusps on Table-case 

 the molar teeth. As shown by the numerous skulls of 8 - 

 Casnotherium in the collection (Fig. 24), there is often a 

 slight gap between its canine tooth and the premolars. 

 The Xiphodontidae are small two-toed animals from the 

 Upper Eocene and Oligocene of England, France, and 

 adjoining countries. Bichodon (Fig. 26) is a typical genus. 

 The Oreodontidae are slightly more advanced ruminants 

 ranging from the Upper Eocene to the Upper Miocene in 

 North America. Fine skulls of Oreodon are exhibited, 

 showing the lower canine tooth shaped like an incisor, while 

 the foremost premolar is enlarged to usurp its function. 



The nearest surviving relatives of these primitive 

 ruminants are the little chevrotains, or Tragulidse, which 

 are now found only in the marshes of the Indo-Malayan 

 region and western Africa. They never possess horns, but 



Fig. 25. — Side-view of skull and mandible of existing Ohevrotain (Tragulus 

 javamicus), from the Malayan region ; reduced in size. 



they agree with the giraffes, deer, and antelopes in having 

 lost their upper front teeth (Fig. 25). Fossil remains of the 

 family are exhibited in Table-case 8. Prodremotherium, 

 from the Oligocene of France, is essentially similar to the 

 living Tragulus, with the enlarged upper canine teeth. 

 Dorcatherium, of which a fine skull is shown from the Lower 

 Pliocene of Eppelsheim, Hesse-Darmstadt, is apparently 

 identical with the living Hymmoschus. 



Of the true ruminants the Tylopoda, or camels and Pier-case 

 llamas, seem to have originated in North America, where 13 - 

 they can be traced back by fossils from the Pliocene and 

 Miocene formations to a little gazelle-shaped creature of the 

 Oligocene period, Poebrotherium. This small animal, of 

 which a skull and limbs are exhibited in Pier-case 13, has a 

 more nearly complete set of teeth than the modern camels, 

 and the basal bones in its feet are not entirely fused together. 



D 2 



