NATURAL THEOLOGY. 113 



nowever, it is considerably varied; but with a 

 strict reference to the conveniency of the animal. 

 For, whereas in quadrupeds the number of verte- 

 brae is from thirty to forty, in the serpent it is 

 nearly one hundred and fifty: whereas in men 

 and quadrupeds the surfaces of the bones are flat, 

 and these flat surfaces laid one against the other, 

 and bound tight by sinews ; in the serpent, the 

 bones play one within another, like a ball and 

 socket,* so that they have a free motion upon one 

 another in every direction : that is to say, in men 

 and quadrupeds, firmness is more consulted ; in 

 serpents, pliancy. Yet even pliancy is not ob- 

 tained at the expense of safety. The back-bone 

 of a serpent, for coherence and flexibility, is one 

 of the most curious pieces of animal mechanism 

 with which we are acquainted. The chain of a 

 watch (I mean the chain which passes between 

 the spring-barrel and the fusee,) which aims at the 



different portions or divisions of it, as these portions are required 

 to admit of more or less freedom of motion. In the hare, as men- 

 tioned in the text, the spine is beautifully accommodated to the 

 motion in running. In the cat-kind, as the leopard or tiger, it has 

 a lateral mobility, quite different from its stnicture in the horse oi 

 the stag. In the boar, the vertebrae are unusually firm, and the 

 processes enormously extended, to give strength to the union with 

 the head, and to direct the action of the muscles upon the head, so 

 that he may tear up strong roots and possess his defence in his 

 powerful tusks. In short, as far as the spine is required to ac- 

 commodate itself to the motions of the trunk, it is varied with as 

 fine an adjustment as the furthest bone of the toe or finger. 



* Der. Phys. Theol. p. 396. 

 10* 



