MAMMALIA RODENTIA. 523 



liess modifications of siriicture that have been 

 executed ia conformity with those plans, I am 

 able particularly to notice only such as are most 

 remarkable. 



§ 8. Rodeutia. 



As the tribes of mammalia we have hitherto 

 examined employ the anterior extremities for 

 the purposes of progression only, they are desti- 

 tute of a clavicle. In most of those which follow, 

 and where a greater developement of the limb 

 confers more extensive and more varied powers 

 of motion, applicable to a greater range of objects, 

 this bone is found. In the greater number, 

 however, it is merely in a rudimental state ; that 

 is, developed only to a certain extent, one portion 

 being bony, and the rest cartilaginous ; as if the 

 ossification had been arrested at an early stage. 

 These imperfect clavicles are too short to connect 

 the scapula with the sternum ; the rest of the 

 space being eked out by cartilage, and by liga- 

 ments : but still they are of great use in affording 

 points of attachment to the muscles of the limb, 

 and giving them the advantage of acting by a 

 rigid lever. The carnivorous tribes, wdiich make 

 considerable use of their fore paws in striking 

 and seizing their prey, have clavicles of this 

 description. Those quadrupeds which have to 



