THE DIAPHRAGM 24! 



viscera (within certain limits) in their respective 

 places ; and it strengthens the abdominal cavity 

 altogether by its uninterrupted extension everywhere 

 through and around it. 



THE DIAPHRAGM. 

 PLATE IX, FIG. i, h. 



This forms a fleshy and tendinous partition, divid- 

 ing the cavity of the chest from that of the abdomen. 

 It is of a broad circular form flattened from before 

 backwards ; its front surface is convex, and concave 

 behind ; divided or forked above, and having two 

 elongations or appendices extending backwards, with 

 pointed extremities. On that side next the chest it is 

 invested by the membrane which covers the lungs, 

 and towards the belly by that which covers the 

 intestines. It adheres to the spine, the ribs, and the 

 breastbone, by strong muscular fibres. Its structure 

 is fleshy and tendinous. The fleshy parts are those 

 which form the circumferent portions of the large 

 muscle, and the principal part of the crura or ap- 

 pendices. The tendinous parts consist of a thin 

 circular expansion, occupying the middle of the 

 larger muscle, and uniting that with the lesser. 

 Through the muscle are seen three remarkable 

 openings, an upper one in the interspace between 

 the crura for the passage of the aorta ; one a little 

 lower, formed by the decussation of the crura for the 

 oesophagus ; and the third, or lower one, perforating 

 the cordiform, or heart-shaped tendon, for the re- 

 ception of the posterior vena cava. 



The diaphragm is the chief agent in inspiration ; 

 it acts in opposition to the abdominal muscles, which 

 are the chief expiratory powers. By the contraction 



Q 



