62 • ON THE REVOLUTIONS OF 



clusively, flesh to cut. Their roots should be the more solid, as they 

 have more and larger bones to break. All these circumstances will in 

 like manner influence the developement of all those parts which serve 

 to move the jaw. 



That the claws may seize the prey, they must have a certain mo- 

 bility in the talons, a certain strength in the nails, whence will result 

 determinate formations in all the claws, and the necessary distribution 

 of muscles and tendons ; it will be necessary that the fore-arm have a 

 certain facility of turning, whence again will result determinate for- 

 mation in the bones which compose it ; but the bone of the fore-arm, 

 articulating in the shoulder-bone, cannot change its structure, without 

 this latter also change. The shoulder-blade will have a certain de- 

 gree of strength in those animals which employ their legs to seize 

 with, and they will thence obtain peculiar structure. The play of all 

 these parts will require certain properties in all the muscles, and the 

 impressions of these muscles so proportioned will more fully determine 

 the structure of the bones. 



It may be seen that we could draw equally just conclusions for the 

 hinder quarters, which contribute to the rapidity of the general move- 

 ments ; as to the formation of the body, the shape of the vertebra?, 

 which influence the ease and flexibility of the motions ; as to the 

 form of nasal bones, of the socket of the eye, of the ear, whose mutual 

 relation to the perfection of the sense of smelling, seeing, and hearing, 

 are so palpable. In a word, the formation of the tooth bespeaks the 

 structure of the articulation of the jaw, that of the scapula, that of the 

 claws, just as the equation of a curve involves all its properties ; and 

 in taking each property separately, as the basis of a particular equa- 

 tion, we should find again both the ordinary equation and all the other 

 certain properties : so the claw, the scapula, the articulation of the 

 jaw, the thigh bone, and all the other bones separately considered, re- 

 quire the certain tooth, or the tooth requires them reciprocally ; and 

 beginning with any one, he who possessed a knowledge of the laws of 

 organic economy, would detect the whole animal. 



This principle is sufficiently self-evident, in the usual acceptation, 

 not to require a farther demonstration ; but when we come to apply it, 

 there are many cases in which our theoretic knowledge of the mutual 

 relations of the structure would not be sufficient, if it were not sup- 

 ported by observation. 



We see, for instance, very plainly that hoofed animals must all be 

 herbivorous, since they have no means of seizing upon their prey ; we 

 see also that, having no other use for their fore-feet than to support 

 their bodies, they have no occasion for so powerfully-framed a shoulder; ' 



