SERPENTS. 



401 



the spine of the Coluber natrix. These vertebrae 



are all united by ball and 

 socket joints, as in the 

 adult batrachia ; the pos- 

 terior rounded eminence 

 of each vertebra being re- 

 ceived into the anterior 

 surface of the next. Fig. 

 202 is a view of this por- 

 tion of the skeleton in the 

 Boa constrictor, showing 

 also the articulation of the 

 ribs with the vertebrae. 

 While provision has thus 

 been made for extent of motion, extraordinary care 

 has at the same time been bestowed upon the 

 security of the joints. Thus we find them ef- 

 fectually protected from dislocation, by the locking 

 in, above and below, of the articular processes, and 

 by the close investment 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 flexion, but to 

 limit the vertical and longitudinal motions ; and 

 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 curvature. 

 The presence of a sternum, restraining the motions 

 of the ribs, would have impeded all these move- 

 ments, and would have also been an insurmountable 

 bar to the dilatation of the stomach, which is ren- 



VOL. I. D D 



