450 



THE MECHANICAL FUNCTIONS. 



Numerous as are the vertebrae of the eel, the 

 spine of which consists of above a hundred, that 

 of serpents is in general formed of a still greater 

 number. In the rattle-snake (Crotaliis horridus) 

 there are about two hundred ; and above three 

 hundred have been counted in the spine of the 

 Coluber natrix. These vertebrae are all united 



by ball and socket joints, 

 as in the adult batrachia ; 

 the posterior rounded emi- 

 nence of each vertebra 

 being received into the 

 anterior surface of the 

 next. Fig. 202 is a view 

 of this portion of the ske- 

 leton in the Boa con- 

 strictor, showing the arti- 

 culation 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 effectually 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 



