144 



ELEMENTARY PHYSIOLOGY 



elastic lungs to the required extent, and to prevent the 

 formation of any vacuum between the two pleurte. This 

 drawing of air into the lungs constitutes an inspiration. 



Fio. 47.— The Diaphragm of a Doo viewed from the Lower or 

 Abdominal Side. 



V.C.I, the vena cava inferior; 0, the oesophagus; Ao. the aorta ; the 

 broad white teiidinois middle (B.B.H) is easily distinguished from the 

 radiating muscular fibres (.4..i.ji) which pass down to the ribs and into 

 the pillars (C*. /)) in front of the vcrtcbrse. 



At the end of each inspiration the diaphragm ceases to 

 contract and the external intercostal muscles relax. So 

 much of the elasticity of the lungs as was called into 

 play by the contraction of the diaphragm and the 



