vi.] RODENTIA. 67 



rudimentary, as in Desmodus ; sometimes elongated, but 

 composed of long, simple, slender, cylindrical vertebral 

 bodies; and generally enclosed in the interfemoral cuta- 

 neous expansion. 



Among the different members of the order Rodentia, 

 there are great differences in the condition of the caudal 

 vertebrae. 



In the Hares, Guinea Pigs, Capybara, &c, the tail is 

 almost rudimentary. In the Cape Jumping Hare (Pedetes) 

 it is nearly as long and powerful as that of a Kangaroo, 

 with well-developed chevron bones. 



In the true Porcupines the tail is generally short j but in 

 some allied genera (Tree Porcupines) it is much elongated 

 and prehensile. 



In the Beaver {Castor) there are 25 caudal vertebrae, all 

 short, broad, and depressed, and with wide transverse pro- 

 cesses, becoming double (anterior and posterior) about the 

 middle of the tail, not by development of a new process, 

 but by gradual division of the one existing in the anterior 

 region. 



In the Ungulata, the tail is variable in length, but of 

 simple character and function ; it is never prehensile, 

 nor has it ever chevron bones, although occasionally, as 

 in the Ox, a pair of well-developed hypapophyses may be 

 produced so as to meet in the median line, enclosing a 

 small canal. 1 The vertebrae are most numerous in the 

 Oxen, and least so in some Deer, especially Moschus, in 

 which animal the tail is quite rudimentary. 



The Elephant has a long tail, composed of 31 vertebrae 

 of simple character, without chevron bones. 



In the Hyrax the tail is almost rudimentary. 



1 The Eocene Anoplotherium appears to have had chevron bones, 

 beneath the vertebras of its long tail. 



F 2 



