RESPIRATION. 181 



while on the other hand, if placed in imitation of the position of the 

 internal intercostals (Fig. 157, E F), i. e., passing downwards and back- 

 wards, they depress them (Fig. 157, E' F'). 



The explanation of the foregoing facts is very simple. The intercos- 

 tal muscles, in contracting, merely do that which all other contracting 

 fibres do, viz., bring nearer together the points to which they are 

 attached; and in order to do this, the external intercostals must raise 

 the ribs, the points C and D (Fig. 156) being nearer to each other when 

 the parallel bars are in the position of the dotted lines. The limit of 

 the movement in the apparatus is reached when the elastic band extends 

 at right angles to the two bars which it connects the points of attach- 

 ment 0' and D' being then at the smallest possible distance one from 

 the other. 



The internal intercostals (excepting those fibres which are attached to 

 the cartilages of the ribs) have an opposite action to that of the external. 

 In contracting they must pull down the ribs, because the points E and 

 F (Fig. 157) can only be brought nearer one to another (Fig. 157, E' F') 

 by such an alteration in their position. 



On account of the oblique position of the cartilages of the ribs with 

 reference to the sternum, the action of the inter-cartilaginous fibres of 

 the internal intercostals must, of course, on the foregoing principles, 

 resemble that of the external intercostals. 



In tranquil breathing, the expansive movements of the lower part of 

 the chest are greater than those of the upper. In forced inspiration, on 

 the other hand, the greatest extent of movement appears to be in the 

 upper antero-posterior diameter. 



Muscles of Extraordinary Inspiration. In extraordinary or 

 forced inspiration, as in violent exercise, or in cases in which there is some 

 interference with the due entrance of air into the chest, and in which, 

 therefore, strong efforts are necessary, other muscles than those just 

 enumerated, are pressed into the service. It is very difficult or impossi- 

 ble to separate by a hard and fast line, the so-called muscles of ordinary 

 from those of extraordinary inspiration; but there is no doubt that the 

 following are but little used as respiratory agents, except in cases in 

 which unusual efforts are required the scaleni muscles, the sternomas- 

 toid, the serratus magnus, the pector ales, and the trapezius. 



Types of Respiration. The expansion of the chest in inspiration 

 presents some peculiarities in different persons. In young children, it 

 is effected chiefly by the diaphragm, which, being highly arched in ex- 

 piration, becomes flatter as it contracts, and, descending, presses on the 

 abdominal viscera, and pushes forward the front walls of the abdomen. 

 The movement of the abdominal wall being here more manifest than that 

 of any other part, it is usual to call this the abdominal type of respira- 

 tion. 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 



