434 MOVEMENTS OF INSPIRATION. [Book ii. 



that movement in the lower part of the chest and abdomen 

 largely characteristic of male breathing, which is hence called 

 diaphragmatic ; the latter causes the movement of the upper 

 chest largely characteristic of female breathing, which is called 

 costal. These two main factors are assisted by less important 

 and subsidiary events. 



Even in the female human subject, the share taken in respi- 

 ration by the diaphragm is an important one, in the male the 

 diaphragm must be regarded as the chief respiratory agent, and 

 in some animals its use, for this purpose, is so prominent that 

 the movements of the ribs may in normal breathing be almost 

 neglected. In the rabbit for instance, in normal breathing, 

 almost all the respiratory work is done by the contractions of 

 the diaphragm. 



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 natter, 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 

 abdominal 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. 



§ 263. 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 articulation, 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 forward. 

 The rib may in fact be regarded as a radius, moving on the ver- 

 tebral articulation as a centre, and causing the sternal attach- 

 ment to describe an arc of a circle in the vertical plane of the 

 body ; as the rib is carried upwards from an oblique to a more 

 horizontal position, the sternal attachment must of necessity be 

 carried farther away in front of the spine. Since all the ribs 

 have a downward slanting direction, they must all tend, when 

 raised towards the horizontal position, to thrust the sternum 



