REPTILES 1386 



and of progressive motion, it is necessary that the 

 spine should be rendered extremely flexible, so as to 

 adapt itself to a great variety of movements. This 

 extraordinary flexibility is given, first, by the sub- 

 division of the spinal column into a great number 

 of small pieces; secondly, by the great freedom of 

 their articulations; and thirdly, by the peculiar mo- 

 bility and connections of the ribs. 



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 (Crotalus horridus) there are about 

 two hundred; and above three hundred have been 

 counted in the spine of the Coluber natrix. These 

 vertebra? 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 an- 

 terior surface of the next. 



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 

 prosesses, are such as to allow of free lateral flex- 

 ion, but to limit the vertical and longitudinal mo- 

 tions: 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 



