RESPIRATION 



37 



from side to side and from back to front when they 

 are lifted (Fig. 23 and 24). 



Fig. 22.— Diagram illustrating the position of the diaphragm, A, when relaxed ; B, 

 when contracted. 



Fia. 23.— Diagram illustrating the 

 dorso-ventral increase in the di- 

 ameter of the thorax when the 

 ribs are raised. (From Martin.) 

 ab, vertebral column; c, d, two 

 ribs in expiration; c', d', their 

 position in inspiration ; st, ster- 

 num in expiration; st', sternum 

 in inspiration. 



Fig. 24.— Diagram illustrating the posi- 

 tion of the chest in A, expiration and 

 B, inspiration. (From Fitz.) 



These inuscles are stimulated when there is an excess 

 of carbon dioxide in the blood. They therefore con- 



