RESPIRATION 



for the other muscles involved. The serrati postici superiores assist the above 

 and also raise the third, fourth, and fifth ribs. The levatores costarum longi 

 and brevi elevate and evert all the ribs from the first to the tenth. 



In extraordinary or forced inspiration, which may be due either to violent 

 exercise or to interference with the due entrance of air into the lungs, all the 

 above muscles act more strongly. The diaphragm descends lower, the 

 scaleni raise the first and second ribs instead of merely fixing them, as in 

 ordinary respiration, as do also the sterno-cleido-mastoids. These, together 

 with the sacro-spinales which straighten the spine, increase the vertical 

 diameter. The trapezii and the rhomboidii assist in increasing the antero- 



FiG. 230. Diagram of Axes of Movement of Ribs. 



posterior and lateral diameters by fixing the shoulders and thus giving a 

 fixed point for the action of the pectorales and latissimi dorsi. 



The enlargement of the chest during inspiration presents peculiarities 

 in different persons. In children of both sexes the principal muscle in- 

 volved seems to be the diaphragm, and this type of breathing is known as 

 abdominal breathing. In men, the chest and sternum, together with the 

 front wall of the abdomen, are subject to a wide movement; this type of 

 breathing is called the inferior costal. In women, the movement appears 

 less extensive in the lower and more extensive in the upper part of the chest, 

 which is called the superior costal type. This has been shown to be due 

 rather to mode of dress than to a real difference in the sexes (Mosher). 



Expiration. Quiet expiration is a passive act due to the return of 

 the thorax and its contained lungs to their normal position when the mus- 

 cles involved in inspiration relax. This elastic recoil is sufficient in ordinary 

 quiet breathing to expel air from the lungs. In forced expiration, however, 



