592 THE MECHANICAL FUNCTIONS. 



cribed, a projecting piece of bone, extending 

 upwards from the crown of the arch, and deno- 

 minated the spinous process (s, s). The sharp 

 ridge that runs along the middle of the back of 

 a quadruped, is formed by the continued series 

 of these processes. There are also, on the sides 

 of the vertebrae, two other projecting pieces, 

 which are denominated the transverse processes 

 (t), and which serve as levers for bending the 

 column laterally, that is, either to the right or to 

 the left. All these component parts of the spine 

 are subject to considerable modifications, in dif- 

 ferent tribes of animals, according to the par- 

 ticular mechanical circumstances of the system, 

 and to the particular intentions of their for- 

 mation. 



There is scarcely any part of the osseous 

 fabric of which the variations better illustrate 

 the strict unity of plan and the beautiful law of 

 gradation observed by nature in all her opera- 

 tions, than the spine. In studying the various 

 modifications which this part of the skeleton 

 undergoes, it will be useful to bear in mind the 

 principles, which appear to regulate its forma- 

 tion, and which Geoftroy St. Hilaire has de- 

 duced by following the history of its early 

 growth, and noticing the order in which its 

 several parts are developed.* In common with 



* Memoires du Museum, ix. 79 and 89. 



