ELASTIC RECOIL OF LUNGS AND CHEST. 209 



respiration when the lower part of the chest is encroached 

 upon by the pregnant uterus. MM. Beau and Maissiat 

 call the former the inferior costal, and the latter the superior 

 costal, type of respiration ; but the annexed diagrams will 

 explain the difference better than the names will, for these 

 imply a greater diversity than naturally exists in the 

 modes of inspiration. 



From the enlargement produced in inspiration, the chest 

 and lungs return in ordinary tranquil expiration, by their 

 elasticity ; the force employed by the inspiratory muscles in 

 distending the chest and overcoming the elastic resistance 

 of the lungs and chest-walls, being returned as an expira- 

 tory effort when the muscles are relaxed. This elastic 

 recoil, chiefly of the rib-cartilages, but also of the lungs 

 themselves, in consequence of the elastic tissue which they 

 contain in considerable quantity, is sufficient, in ordinary 

 quiet breathing, to expel air from the chest in the inter- 

 vals of inspiration, and no muscular power is required. 

 In all voluntary expiratory efforts, however, as in speaking, 

 singing, blowing, and the like, and in many involuntary 

 actions also, as sneezing, coughing, etc., something more 

 than merely passive elastic power is of course necessary, 

 and the proper expiratory muscles are brought into action. 

 By far the chief of these are the abdominal muscles, which, 

 by pressing on the viscera of the abdomen, push up the 

 floor of the chest formed by the diaphragm, and by thus 

 making pressure on the lungs, expel air from them through 

 the trachea and larynx. All muscles, however, which 

 depress the ribs, must act also as muscles of expiration, 

 and therefore we must conclude that the abdominal 

 muscles are assisted in their action by the greater part of 

 the internal intercostals and triangularis sterni, the ser- 

 ratus posticus inferior, etc. When by the efforts of the 

 expiratory muscles, the chest has been squeezed to less 

 than its average diameter, it again, on relaxation of the 

 muscles, returns to the normal dimensions by virtue of its 



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