186 HAND-BOOK OF PHYSIOLOGY. 



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. 157) 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 oi; attachment C' 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 exter- 

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

 and F (Fig. 158) can only be brought nearer one to another (Fig. 158, 

 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, re- 

 semble 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 im- 

 possible to separate by a hard and fast line, the so-called muscles of ordi- 

 nary 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 pectorales, 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 expiration, 

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

 viscera, and pushes forward the front walls of the abdomen. The move- 

 ment 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 for- 

 ward 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). (See Figs. 159, 

 160.) 



B. Expiration. From the enlargement produced in inspiration, 

 the chest and lungs return in ordinary tranquil expiration, by their elas- 

 ticity; the force employed by the inspiratory muscles in distending the 



