SERPENTS. 313 



ally protected from dislocation by the locking; in, above 

 and below, of the articular processes, and by the close in- 

 vestment of the capsular ligaments. The direction of the 

 surfaces of these processes, and the shape and length of the 

 spinous processes, are such as to allow of free lateral flex- 

 ion, but to limit the vertical and longitudinal motions: and 

 whatever degree of freedom of motion may exist between 

 the adjoining vertebra?, 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 

 curvature. The presence of a sternum, restraining the mo- 

 tions of the ribs, would have impeded all these movements, 

 and would have also been an insurmountable bar to the di- 

 latation of the stomach, 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 en- 

 circled within its folds, required the ribs to be moveable la- 

 terally, 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 or- 

 dinary mode of articulation would not have aflforded. The 

 spinous processes in this tribe of serpents are short and wide- 

 ly 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 suppose the 

 lengthened body of a serpent to be capable, it will, at first 

 view, be diflacult to conceive how these simple actions can 

 be rendered subservient to the purposes of progression on 

 land : and yet experience teaches us that few animals advance 

 with more celerity on the surface of the ground, or dart upon 

 their prey with greater promptitude and precision. Tlifiy 



Vol. I. 40 



