390 



2169. A portion of the branch of a tree which has been gnawed by a Beaver, indi- 

 cating the force with which the great incisors act upon the woody tissue. 



The following are parts of the same skeleton of a Canada Beaver (Castor canadensis). 



Hunterian. 



2170. The atlas. 



It is perforated and notched, as in the Porcupine : a tuberosity is developed from the upper 

 and fore part of the neural arch. There is no tubercle on the under part. The hinder arti- 

 cular processes are slightly concave. 



2171. The axis. 



It is short, but high, and the fore part of the base of the strong spine overhangs the odon- 

 toid process. 



2172. The sixth cervical vertebra. 



It is remarkable for its shortness and great breadth. 



2173. The first dorsal vertebra. 



It shows the expansion of the diapophysis, and the impression on its under part for the 

 tubercle of the rib. 



2174. The sixth dorsal vertebra. 



It shows the accessory process developed above the diapophysis. 



2175. The ninth dorsal vertebra. 



The accessory process has expanded : the diapophysis has diminished. 



2176. The thirteenth dorsal vertebra. 



The accessory process has here divided into the anapophysis and metapophysis. 



2177. The fourteenth dorsal vertebra. 



It shows the complete separation of the metapophysis from the diapophysis, and the 

 advancement of the former to above the anterior zygapophysis. 



2178. An anterior lumbar vertebra. 



It shows the development of the diapophysis to an equality of length with the two acces- 

 sory processes. 



