VERTEBRAL COLUIMN. 34.0 



the flexions of the vertebrae upon one another, nor 

 is the continuity of the column in the smallest 

 decree interrupted. 



The motions of the vertebrae upon each other 

 are farther regulated by the mode in which their 

 articular processes, which are the pieces that pro- 

 ject obliquely on each side, play upon each other. 

 These processes, which are seen at a, a, in the pre- 

 ceding figures (177 and 178), are 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 toge- 

 ther, 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 allowing a passage to the 

 spinal marrow, the bodies of the vertebrae (b, Fig. 

 177 and 178), are hollowed out behind into a groove, 

 over which a broad plate of bone is throv.^n 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 pas- 

 sage of the nerves as they issue from the spinal 

 marrow. All these circumstances are visible in the 

 figures, particularly in the section, Fig. 1 79, where 

 c, c, is the canal for the spinal marrow, and in 

 which the apertures just mentioned are distinctly 

 seen, at o, o. 



