310 DIFIEEEXCE BETWEEN 



firmness \^■ith which these three bones are united to 

 each other is always in proportion to the power of 

 flight in the bird. In no bird of powerful wing can 

 any of them be dislocated from the other two without 

 fracture ; and in old eagles and hawks, the portion of 

 cartilaginous matter by which they are united passes 

 so completely into bone, though bone which remains 

 a little flexible, that they cannot be detached from 

 each other by maceration in water. 



It is worthy of remark, as affording a beautiful 

 instance of that provision of nature by means of which 

 the vital parts of animals are always protected from 

 injury even in their most violent actions, if those 

 actions are natural, or essential to the accomplish- 

 ment of those purposes which their Creator has 

 ordained them to accomplish, that the anterior extre- 

 mities of no vertebrated animal are articulated upon 

 the spinal column. This is v^ery remarkably the case 

 in birds of powerful wing. 



In mammalia, the articulation of the humerus is 

 always upon the scapula only; they want the coracoid 

 bones entirely, and in those species which use the 

 fore legs only in walking, the clavicles are wanting. 

 Even in those species, as in the quadrumana, which 

 have the clavicles most perfectly developed, the 

 office of these bones is secondary, chiefly that of 

 keeping the shoulder-joints apart from each other, 

 so that the animals may stretch their fore-legs, or 

 arms, at right angles to the mesial plane of the body, 

 and not use them parallel to that plane only, as is the 

 case with those mammalia which employ the fore legs 

 only in walking. 



In the mammalia, the scapular bone is flattened 

 and extended to the shape of a triangular plate, and 

 it is furnished with a spine, or elevated keel of bone. 



