320 MOVEMENTS OF INSPIRATION. [BOOK 11. 



the diaphragm are watched by means of an inserted needle, the 

 upper surface of that organ is seen to descend at each inspiration, 

 the anterior walls of the abdomen bulging out at the same time. 

 In the female human subject, the movement of the upper part of 

 the chest is very conspicuous, the breast rising and falling with 

 every respiration ; in the male, however, the movements are almost 

 entirely confined to the lower part of the chest. In laboured 

 respiration all parts of the chest are alternately expanded and 

 contracted, the breast rising and falling as well in the male as in 

 the female. We have now to consider these several movements in 

 greater detail, and to study the means by which they are carried 

 out. 



Inspiration. There are two chief means by which the chest is 

 enlarged in normal inspiration, viz. the descent of the diaphragm 

 and the elevation of the ribs. The former causes that movement 

 in the lower part of the chest and abdomen so characteristic of 

 male breathing, which is called diaphragmatic ; the latter causes 

 the movement of the upper chest characteristic of female breath- 

 ing, which is called costal. These two main factors are assisted by 

 less important and subsidiary events. 



The descent of the diaphragm is effected by means of the 

 contraction of its muscular fibres. When at rest the diaphragm 

 presents a convex surface to the thorax; when contracted it 

 becomes much flatter, and in consequence the level of the chest- 

 floor is lowered, the vertical diameter of the chest being pro- 

 portionately enlarged. In descending, the diaphragm presses on 

 the abdominal viscera, and so causes a projection of the flaccid ab- 

 dominal walls. From its attachments to the sternum and the false 

 ribs, the diaphragm, while contracting, naturally tends to pull the 

 sternum and the upper false ribs downwards and inwards, and the 

 lower false ribs upwards and inwards, towards the lumbar spine. 

 In normal breathing, this tendency produces little effect, being 

 counteracted by the accompanying general costal elevation, and by 

 certain special muscles to be mentioned presently. In forced 

 inspiration however, and especially where there is any obstruction 

 to the entrance of air into the lungs, the lower ribs may be 

 so much drawn in by the contraction of the diaphragm, that the 

 girth of the trunk at this point is obviously diminished. 



The elevation of the ribs is a much more complex matter than 

 the descent of the diaphragm. If we examine any one rib, such as 

 the fifth, we find that while it moves freely on its vertebral arti- 

 culation, it inclines when in the position of rest in an oblique 

 direction from the spine to the sternum ; hence it is obvious that 

 when the rib is raised, its sternal attachment must not only 

 be carried upward, but also thrown forwards. The rib may in fact 

 be regarded as a radius, moving on the vertebral articulation as a 

 centre, and causing the sternal attachment to describe an arc of a 



