752 MANUAL OF ZOOLOGY. 



Upper Miocene, but the best known fossil member of this 

 family is the Cave- hyaena (H. spelceti) of the Post-pliocene, 

 which is probably but a variety of the living Hycena crocuta. 



The family of the Canidce seems to be one of the oldest of 

 the families of the Carnivora, and is represented in the Eocene 

 period by several genera (Cynodictis, Galethylax, &c.) In the 

 later Tertiary and Post-tertiary, various extinct forms of this 

 family are likewise known to occur. 



The family of the Hy<Knodontid& comprises certain extinct 

 Eocene Carnivores {Hycenodon, Pterodon, &c.), in which there 

 is the anomalous feature that all the prasmolars and molars 

 have cutting edges. 



Lastly, the family of the Felidce appears to commence in the 

 Eocene period, the best-known extinct type of this family being 

 the genus Machairodus including the so-called "sabre-toothed 

 Tigers." In this wonderful genus we are presented with the 

 most highly carnivorous type of all known beasts of prey. Not 

 only are the jaws shorter in proportion than those of the most 

 rapacious of existing Felidce, but the canine teeth are of enor- 

 mous size, compressed and sabre-shaped, and having their mar- 

 gins finely serrated. Species of Machairodus must have been 

 as large as the living Lion ; and the genus has an extraordin- 

 ary range both in time and space, occurring in North and South 

 America, in India, and in Europe, and extending from the 

 Miocene to the Human period. 



CHAPTER LXXVI. 

 RODENTIA. 



ORDER XIII. RODENTIA. The thirteenth order of Mammalia 

 is that of the Rodentia, or Rodent Animals, often spoken of as 

 Glires, comprising the Mice, Rats, Squirrels, Rabbits, Hares, 

 Beavers, &c. 



The Rodentia are characterised by the possession of two long 

 curved incisor teeth in each jaw, separated by a wide interval from 

 the molars. The lower jaw never has more than two of these in- 

 cisors, and the tipper jaw very rarely ; but sometimes there are 

 four upper incisors. There are no canine teeth, and the molars 

 and prcemolars are few in miniber (rarely more than four on each 

 side of the jaw}. The feet are usually furnished with five toes 

 each, all of which are armed with claws ; and the hallux, when 



