RODENTIA. 463 



which have to execute still more complex actions 

 with their fore feet, have perfect clavicles, extend- 

 ing from the shoulder to the chest, and connecting 

 the bones of the anterior extremity with the general 

 framework of the skeleton. This is the case in a 

 large proportion of the family of Rodentia, such as 

 the Squirrel, which employs its paws for holding- 

 objects; and the Beaver, which likewise makes 

 great use of its fore feet, which might almost be 

 termed hands, in building its habitation. Animals 

 that dwell in trees, and require to grasp with force 

 the branches in moving along them, such as the 

 Sloth, have also distinct clavicles. Animals which 

 rake or dig the ground, as the Mole, the Ant-eater, 

 and the Hedge-hog are all provided with these 

 bones, which, by keeping the shoulders at the 

 same constant distance from the trunk, and afford- 

 ing a firm axis for the rotatory motions of the limb, 

 materially assist them in the performance of these 

 actions. 



The beaver presents a singular modification in 

 the structure of the tail, which is expanded into a 

 flattened oval disk, covered by a skin beset with 

 scales ; and which is used by the animal as a 

 paddle for supporting itself on the water, or for 

 quickly diving to the bottom. There does not 

 appear to be any truth in the opinion commonly 

 entertained, that the Beaver employs its tail as a 

 trowel for plastering the mud walls of its dwelling. 



