SERPENTS. 451 



whatever degree of freedom of motion may exist 

 between the adjoining vertebrae, that motion 

 being multiplied along the column, the flexibility 

 of the whole becomes very great, and admits of 

 its assuming every degree and variety of curva- 

 ture. The presence of a sternum, restraining 

 the motions of the ribs, w ould have impeded all 

 these movements, and would have also been an 

 insurmountable bar to the dilatation of the sto- 

 mach, which is rendered necessary by the habit 

 of the serpent of gorging its prey entire. 



The mode in which the boa exerts a powerful 

 pressure on the bodies of the animals it has 

 seized, and which it has encircled within its 

 folds, required the ribs to be moveable laterally, 

 as well as backwards, in order to elude the force 

 thus exerted. The broad convex surfaces on 

 which they play give them, in this respect, an 

 advantage which the ordinary mode of articula- 

 tion would not have afforded. The spinous pro- 

 cesses in this tribe of serpents are short and 

 widely separated, so as to allow of flexion in 

 every direction. In the rattle-snake, on the 

 other hand, their length and oblique position are 

 such as to limit the upward bending of the spinal 

 column, although, in other respects, its motion is 

 not restricted. The vertebrae at the end of the 

 tail are furnished with broad transverse processes 

 for the attachment of the first joints of the rattle. 



But of whatever variety of flexions we may 



