VERTEBRAL COLUMN. 273 



which are the pieces that project ohllquely on each side, 

 play upon each other. These processes, which are seen at 

 A, A, in the preceding figures (177 and 178) arc of great use 

 in preventing the sudden displacement of the vertebrae; for 

 this effect cannot be produced by any force short of that 

 which would occasion fracture. Any one who will try to 

 dislocate, by sheer force, the spine of a hare or rabbit will 

 find reason to admire the art with which its bones have been 

 locked together, and the skill displayed in combining great 

 flexibility with such powerful resistance to every effort that 

 can be made to separate them. 



For the purpose of allow^ing a passage to the spinal mar- 

 row, tlie bodies of the vertebrae (b, Fig. 177 and 178,) are 

 hollowed out behind, into a groove, over which a broad 

 plate of bone is thrown from the sides of the vertebrae, like 

 the arch of a bridge. The succession of arches, when the 

 vertebrae are joined together, forms a continuous canal, 

 which is occupied by the spinal marrow. Notches, corre- 

 sponding to each other, are left in the sides of each of the 

 arches, forming apertures for the secure passage of the nerves 

 as they issue from the spinal marrow. All these circum- 

 stances are visible in the figures, particularly in the section. 

 Fig. 179, where c, c, is the canal for the spinal marrow, and 

 in which the apertures just mentioned are distinctly seen, at 



o, o. 



In order to give an advantageous purchase to the muscles 

 which are attached to the spine, each vertebra lias, besides 

 the parts above described, a projecting piece of bone, ex- 

 tending upwards from the crown of the arch, and denomi- 

 nated 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 vertebraj, tw^o other projecting pieces, which 

 are denominated the transverse processes (t,) and which 

 serve as levers for bending the column laterally, that is, ei- 

 ther to the right or to the left. All these com])onent parts 

 of the spine are subject to considerable modifications, in dif- 

 ferent tribes of animals, according to the particular mccha- 



VoL. I. 35 



