VERTEBRATE!) ANIMALS. 



as is proved by the fact, that the destruction of the peri- 

 osteum, causes the death and decay of the part over which 

 it was placed. 



SPINE OF THE VERTEBRATA. 



225. The word spine signifies a thorn ; this part of the 

 skeleton being so called, because each piece of which the 

 back bone is formed, has a projecting process outward, 

 making as a whole that prominent ridge so well known as 

 the spine in various animals. Thus by common consent, 

 and long usage, a column made up of many pieces, is not 

 only named after a sharp-pointed instrument, but is spoken 

 of aS a single bone. 



226. This column in the human species, consists of 

 twenty-four distinct bones, named vertebra, from the Latin 

 vertere, to turn, because this part of the skeleton has motion 

 in every direction. 



227. Of these twenty-four pieces, five 



belong to the loins, twelve to the back, Fi s- 63 - 

 and seven to the neck. The whole spinal 

 column is represented by Fig. 63, of 

 which the pieces above 2, and below 1, 

 belong to the neck and loins ; while those 

 between, belong to the back. 



228. The spine is the foundation, or 

 chief mechanical support of the whole 

 skeleton ; and riot only so as giving pro- 

 tection to the spinal cord, w r hich in one 

 sense is a part of the brain, being a con- 

 tinuation of its substance, but is a very 

 essential part with respect to the nervous 

 system. 



229. A single vertebra is shown by 

 Fig. 64, where the lower part, or body, 

 which is somewhat radiated on the surface, 

 is that by which it is joined to its fellow. 

 The elongation s is called the spinous 

 process; and is that which,when the whole 

 are in place, forms the ridge of the spine, 

 pr back. Beside this, there is another pro- 

 jection, t, on each side of the base of the 



