The Framework of the Body 



43 



In the pivot joint a part of one bone fits into a notch in 

 another. The best example of this is the joint between 

 the first and second vertebrae. The radius moves around 

 on the ulna by means of a pivot joint. 

 v 63. Uses of the Bones. The bones serve many impor- 

 tant and useful purposes. The skeleton, a general frame- 

 work, affords protection, support, and 

 leverage to the other bodily tissues. 

 Thus, the bones of the skull and of 

 the chest protect the brain, the lungs, 

 and the heart. The long bones of 

 the limbs are levers to which muscles 

 are attached. 



Bones have many different shapes. 

 Each bone is not only different from 

 all the others, but is also curiously 

 adapted to its particular place and 

 use. 



We have seen how the bones of 

 the cranium are united by sutures, 

 the better to, allow the delicate brain 

 to grow, and to afford it protection 

 from violence. 



The complicated organ of hearing 

 is protected by a winding series of 

 minute apartments in the rock-like 

 portion of the temporal bone. The socket for the eye Jias a 

 jutting ridge of bone around it to guard this organ against 

 injury. Grooves and canals, formed in hard bone, lodge 

 and protect minute nerves and tiny blood vessels. The 

 surfaces of bones are often provided with grooves, sharp 

 edges, and rough projections, for the origin and insertion 

 of muscles. 



FIG. 27. Showing how 

 the Ends of the Bones 

 are shaped to form the 

 Elbow Joint. 



(The cut ends of a few 

 ligaments are seen.) 



