84 



VERTEBRATED ANIMALS. 



nourished, as is proved by the fact, that the destruction 

 of the periosteum, causes the death and decay of the 

 part over which it was placed. 



SPINE OF THE VERTEBRATA. 



The word spine signifies a thorn ; this part of the skel- 

 eton 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 know r n 

 as the spine in various animals. Thus by common con- 

 sent, 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. 



This column, in the human species, consists of twenty- 

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

 tere, to turn, because this part of the skeleton has mo- 

 tion in every direction. 



Of these twenty-four pieces, five belong to the loins, 



Fig. 63. 



twelve to the back, and seven to the 

 neck. The whole spinal column is rep- 

 resented 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. 



The spine is the foundation, or chief 

 mechanical support of the whole skele- 

 ton ; and not only so, as giving protec- 

 tion to the spinal cord, which in one sense 

 is a part of the brain, being a continua- 

 tion of its substance, but is a very essen- 

 tial part with respect to the nervous sys- 

 tem. 



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, or 

 back. Besides this, there is another pro- 

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



