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HAND-BOOK OF PHYSIOLOGY. 



the hinder ends being prevented from performing any upward movement 

 by their attachment to the spine. The movement of the front extremities 

 of the ribs is of necessity accompanied by an upward and forward move- 

 ment of the sternum to which they are attached, the movement being 

 greater at the lower end than at the upper end of the latter bone. 



FIG. 155. Diagram of axes of movement of ribs. 



The axes of rotation in these movements are two; one corresponding 

 with a line drawn through the two articulations which the rib forms with 

 the spine (a b, Fig. 155); and the other, with a line drawn from one of 

 these (head of rib) to the sternum (A B, Fig. 155, and Fig. 156); the 



FIG. 156. Diagram of movement of a rib in inspiration. 



motion of the rib around the latter axis being somewhat after the fashion 

 of raising the handle of a bucket. 



The elevation of the ribs is accompanied by a slight opening out of the 



