The Framework of the Body 



33 



Joined to the lower end of the sacrum is the coccyx, a 

 tapering series of little bones. It derives its. name from 

 a fancied resemblance to the beak of a cuckoo. 



46. The Ribs. The barrel-shaped framework of the 

 chest is in part composed of long, slender, curved bones, 

 called ribs. There are twelve ribs on each side. Each 

 pair is attached to a dor- 

 sal vertebra behind. 



The first seven pairs, 

 counting from the neck, 

 are called the true ribs, 

 and are joined by car- 

 tilages directly to the 

 breastbone. The five 

 lower pairs, called the 

 false ribs, are not directly 

 joined to the breastbone, 

 but are connected, with 

 the exception of the last 

 two, with each other and 

 with the last true ribs by 

 cartilages. These elastic 

 cartilages enable the 

 chest to bear great blows 

 with impunity. Thus a blow on the breastbone is distrib- 

 uted over fourteen elastic arches. The lowest two pairs 

 of false ribs are quite free in front, and for this reason are 

 often called " floating" ribs. 



The ribs are not horizontal, but slope downwards from 

 the backbone, so that when raised or depressed by the strong 

 intercostal muscles, the size of the chest is alternately 

 increased or diminished. This movement of the ribs, as we 

 shall learn later, is of the utmost importance in breathing. 



FIG. 19. Thorax. 

 (Anterior view.) 



