THE HUMAN SKELETON 



83 



of the ribs from above downwards is oblique, forming, as it 

 were, a bundle of hoops playing on each other. 



38. The curve of the ribs diminishes considerably from 

 the first to the twelfth ; the sfecond, however, is usually more 

 curved than the first. The inferior ribs are very flat ; the 

 twelfth is sometimes straight. The external surface of each 

 rib is convex, the internal concave. Each rib on its outer 

 surface near the spine presents an oblique ridge, occasioned 

 by the insertion of a muscle ; and at this point there is a 

 curvature somewhat abrupt, called the angle of the rib. 



Fourth rib ; a, vertebral extremity, called the head, which is connect, 

 ed with the bodies of the two contiguous dorsal vertebrae. At i, the 

 bone is contracted, forming the neck ; c, is the tubercle at the back of 

 the rib, which is articulated with the transverse process of the ver- 

 tebrae ; d, the angle ; e, the sternal extremity ; /, a groove for the inter- 

 costal vessels. This will serve for a general description of the ribs. 



Twelfth rib, nearly straight. 



r* 



39. Sternum. -Between the forward ends of the ribs, 



directly in front of the chest, lies the sternum, or breast- 

 bone.) fit is light and spongy, depending chiefly for its 

 strength on the numerous ligaments which cover it. In tho 

 child, it is divided into eight pieces by cartilaginous portions, 



