144 DESCRIPTION OF THE SKELETON. 



from all ordinary accidents, and also to the organs 

 of hearing, seeing, smelling, and tasting. Protec- 

 tion and not motion being the sole object of its con- 

 struction, the numerous bones of which it is com- 

 posed are joined to each other, not by moveable 

 joints .ilke other bones, but by a kind of dovetailing, 

 which combines the solidity of continuous struc- 

 ture with the advantages which their separation 

 gives in facilitating growth, and interrupting the ex- 

 tension to all, of the injuries inflicted on one. 



The trunk, as will be seen from the annexed cut, 

 consists of the spine a a, the ribs r r, the sternum x, 

 and the pelvis s s. The spine, vertebral column, or 

 back-bone, a a, which supports all the other parts, 

 is a very remarkable piece of mechanism. It is 

 composed in all of twenty-four separate bones 

 called vertebra, from the Latin word verlere to turn, 

 as the body turns upon them as on a pivot. Of 

 these, seven, called cervical vertebrae, belong to 

 the neck ; twelve, connected with the ribs and 

 called dorsal, to the back ; and five, called lumbar, 

 to the loins. The base of the column rests on the 

 sacrum u, which is closely compacted between the 

 bones of the pelvis s s. The vertebrae are firmly 

 bound to each other in such a way as to admit 

 of flexion and extension and a certain degree of 

 rotation, while by their solidity and firm attach- 

 ment to each other great strength is secured. Some 

 conception of this strength may be formed when we 

 consider the enormous loads which some athletic 

 men are able to carry on their shoulders, or raise in 

 their hands ; the whole weight of which is neces- 

 sarily borne by the vertebrae of the loins. As the 

 space occupied by the abdomen gives large outward 

 dimensions to this region of the body, it is only 

 upon reflection that we perceive that the whole 

 force exerted by the human frame in its most stren- 

 uous efforts centres ultimately in the bony column 

 we are now examining 



