CH. XXVI.] MUSCLES OF RESPIRATION 355 



by the scaleni. The greater number of the ribs are attached very 

 obliquely to the spine and sternum. 



The elevation of the ribs takes place both in front and at the 

 sides the hinder ends being prevented from performing any upward 

 movement by their attachment to the spine. The movement of- 

 the front extremities of the ribs is of necessity accompanied by 

 an upward and forward movement of the sternum to which they 

 are attached, the movement being greater at its lower than at its 

 upper end. 



The muscles by which the ribs are raised, in ordinary quiet inspira- 

 tion, are the external intercostals, and that portion of the internal 

 intercostals which is situated between the costal cartilages; and 

 these are assisted by the levatores costarum, and the serratus posticus 

 superior. 



In extraordinary or forced inspiration, additional muscles are 

 pressed into service, such as the sternomastoid, the serratus magnus, 

 the pectorales, and the trapezius. Laryngeal and face muscles also 

 come into play. 



The expansion of the chest in inspiration presents some peculi- 

 arities in different persons. In young children, it is effected chiefly 

 by the diaphragm. The movement of the abdominal walls being here 

 more manifest than that of any other part, it is usual to call this the 

 abdominal type of respiration. In men, together with the descent of 

 the diaphragm, and the pushing forward of the front wall of the 

 abdomen, the chest and the sternum are subject to a wide movement 

 in inspiration (inferior costal type). In women, the movement 

 appears less extensive in the lower, and more so in the upper, part of 

 the chest (superior costal type). 



Expiration. From the enlargement produced in inspiration, the 

 chest and lungs return, in ordinary tranquil expiration, by their 

 elasticity to their previous condition; the force employed by the 

 inspiratory muscles in distending the chest and overcoming the 

 elastic resistance of the lungs and chest-walls, is returned as an 

 expiratory effort when the muscles are relaxed. This elastic recoil 

 of the chest and lungs is sufficient, in ordinary quiet breathing, to 

 expel air from the lungs in the intervals 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 necessary, and the proper 

 expiratory muscles are brought into action. 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 



