i6 



ELEMENTARY PHYSIOLOGY 



means of costal cartilage to the breast-bone a long, flat, and soft 

 bone, the lower part of which is formed of flexible cartilage. It 

 will thus be seen that the ribs, together with the backbone and the 

 sternum, form an elastic framework with movable sides. This 

 acts as a protection to the organs contained in the chest or upper 

 portion of the trunk, and assists largely in the process of respira- 

 tion. 



The ribs are not placed horizontally, but incline downwards 



Fig. 15. The Bony Framework of 

 the Chest, viewed from the 

 right side. (See also fig. 134.) 



i, backbone ; 2, ribs ; 3, breast-bone. 



Fig. 1 6. The Breast-hone. 



A, viewed from before ; B, viewed from the 

 right side ; i, 2, 3, 4, 5, 6 and 7 are the 

 surfaces to which the corresponding costal 

 cartilages are attached. 



from the backbone, so that when they are raised and depressed, 

 as they are during the inspiration and expiration of air in breathing, 

 the capacity of the chest is alternately increased and decreased. 



We may now notice the manner in which the pairs of ribs differ from 

 each other. In the first place we observe that the upper pairs form small 

 arches, and that the size of the arches increases from above downwards, thus 

 the framework formed is somewhat conical. Thejirst seven pairs have their own 

 costal cartilages, connecting them directly with the sternum. They are called 

 true ribs. The eighth, ninth, and tenth pairs are each connected with the 



