386 THE MECHANICAL FUNCTIONS. 



4. Skeleton of the Vertebrata. 



THE purposes to be answered by the Skeleton, 

 in vertebrated animals, resolve themselves into 

 the three following ; first, the affording mecha- 

 nical support to the body generally, and also to 

 different portions of the body ; secondly, the 

 providing a solid basis for the attachments of 

 the muscles which are to effect their movements ; 

 and thirdly, the giving protection to the vital 

 organs, but more particularly to the central parts 

 of the nervous system. Of these the last is the 

 circumstance that has the greatest influence in 

 determining the principles on which the osseous 

 frame- work has been constructed. In the ner- 

 vous system of all the animals coming under the 

 denomination of vertebrata, the spinal marrow, 

 together with the brain, which may, indeed, be 

 considered as the anterior extremity of the spi- 

 nal marrow, only much enlarged by an additional 

 mass of nervous substance, are the most import- 

 ant parts of that system, and the organs which 

 stand most in need of protection from every 

 kind of injury. These two portions of the 

 nervous system, when viewed as composing a 

 single organ, have been denominated the spino- 

 cerebral axis, in contradistinction to the analo- 

 gous parts of the nervous system of articulated 



