49 



point of application to tlie same relative position 

 it would take by active movement, all these effects 

 could be brought about by the movement of the 

 left head condyle, against the passive resistance of 

 the rear point, continued throughout. 



§ 49. As has been already mentioned, the num- 

 ber of S S formed in the elastic rod, as well as 

 their relative proportions, would be dependent on 

 conditions involved in its structure ; so in the 

 snake's body, where these conditions must depend 

 very much on the will of the animal, the number 

 of S S and their proportions may probably be 

 regulated at its pleasure. In man and quadrupeds, 

 however, they are fixed, in both respects by the 

 form of the mechanism. 



§ 50. There is one other set of actions which 

 might be here discussed, viz., those arising from 

 both pairs of diagonal forces acting simultaneously, 

 but, as it seems to us doubtful whether the snake, 

 having no unyielding breast-bone, be capable of 

 using them, and since they may be as well and 

 more conveniently taken up, when speaking of the 

 higher animals, vv^e defer them for the present, ex- 

 cepting, so far as they are spoken of in § 71 and 

 onward. 



§ 51. In the different facings of the protuber- 



