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A Manual of Veterinary Physiology. 



the lungs in expelling the air. The compression which 

 the abdominal contents undergo in inspiration, causes the 

 abdominal muscles to descend ; this is now relieved, and 

 the process of expiration is further assisted by the con- 

 traction of these muscles, which forces the viscera forward 

 against the diaphragm. 



The action of the muscles of the chest during respiration 



Fig. 4.— Horizontal Section oe the House's Chest, looked at 

 kkom above, illustrating the movements of the dlaphragji. 



</, right lung ; />, left lung. 1. Position of the diaphragm during deep 

 expiration : c, liver during deep expiration ; d, stomach during 

 deep expiration ; e, spleen during deep expiration. 2. Position of 

 diaphragm during deep inspiration : <:', position of liver; </', of 

 stomach ; e', of spleen during deep inspiration ; /, posterior vena 

 cava as ix, passes through the diaphragm (Sussdorfj. 



has been much disputed. The external intercostals doubt- 

 less, from the direction taken by their fibres, draw the 

 ribs forward, and by so doing increase the transverse 

 diameter of the chest ; in this respect they are regarded as 

 inspiratory muscles. The internal intercostals, the Hbres of 

 which run in an opposite direction to the external, draw the 

 ribs backwards and act as muscles of expiration ; and speak- 



