MAMMALIA. 35 



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

 the molar teeth. As shown by numerous skulls of Csenothe- ®* 



rium (Fig. 24), there is often a slight gap l)etween 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. Dichodon (Fig. 26) 

 is a typical genus. The Oreodontidae are more advanced 

 ruminants ranging from the Upper Eocene to the Upper 

 Miocene in Xorth America. Skulls of Orcodon are exhibited, 

 showing the lower canine tooth shaped like an incisor, while 

 the foremost premolar is enlarged to usurp its function. The 

 Protoceratidae are an Oligocene North American family, in 

 which the males bear at least two pairs of bony bosses (or 

 " horns ") on the head. 



The nearest surviving relatives of these primitive 

 ruminants are the little chevrotains, or Tragulidse, which 

 are now found only in tlie marshes of the Indo-j\Ialayan 

 region and western Africa. They never possess horns, but 



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

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



tliey agree with the giraffes, deer, and antelopes in having no 

 upper front teeth (Fig. 25). Prodremotherium, from the 

 Oligocene of France, is essentially similar to the living 

 7'raf/u/ns, with tlie enlarged upper canine teeth. Dorcathe- 

 rhnn, of which a fine skull is shown from the Lower Pliocene 

 of Ep])('lsheim, Hesse-Darmstadt, is apparently identical 

 with the living Hyn'moschus. 



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

 llamas, seem to have originated in Xorth America, where ^* 

 they can be traced liack by fossils from the Pliocene and 

 Miocene formations to a little ga2:elle-sha])ed creature of the 

 Oligocene period, Poehrothn'inm. This small animal, of 

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

 UKjre nearly complete set of teeth than the modern camels, 



D 2 



