THE BODY.] 



PHYSIOLOGY, 



n 



the sides are strengthened by the ribs, long thin hoops 

 of bone which are fastened to the backbone behind 

 and meet in front in a firm hard part, partly bone, partly 

 cartilage, called the sternum. 



But this backbone is not made of one long straight 

 piece of bonc« If it were you would never be able 

 to bend your body. To eftable you to do this it is 

 made up of ever so many little flat round pieces of 

 bone, laid one a-top of the other, with their flat sides 

 carefully joined togethejr, like so many bungs stuck 

 together. Each of these little round flat pieces of 

 the backbone is called a vertebra, and is of a very 

 peculiar shape. Suppose you took a bung of bone, 

 and fastened on to one side of its edge a ring 

 of bone. That would represent a vertebra. The 

 solid bung is what is called the body^ and the hollow 

 ring is what is called the arch of the vertebra. ITow 

 if you put a number of these bodies together one 

 upon the top of the other, so that the bodies all came 

 together and the rings all came together, you would 

 have something very like the vertebral column (see 

 Frontispiece, also Fig. 2). The bungs or bodies 

 would make a solid jointed pillar, and the rings or 

 arches would make together a tunnel or canal. And 

 that is really what you have in the backbone. Only 

 each vertebra is not exactly shaped like a bung and 

 a ring ; the body is very like a bung, but the arch is 

 rough and jagged, and the bodies are joined together 

 in a particular way. Still we have all the bodies of 

 the vertebrae forming together a solid pillar which 

 gives support to the trunk \ and the arches forming 

 together a tunnel or canal which is called the spinal 

 canal, (Fig. 2, C,S^ the use of which we shall see 



