Human physiology : designed for colleges and the higher classes in schools and for general reading . as they occur in inspiration. It is supposed that inordinary expiration, there is little, if any, muscular action—that as the diaphragm, which in inspiration pushed down thestomach and liver, and thus thrust out the walls of the ab-domen, ceases to contract and relaxes, the mere elasticity ofthe parts below, and especially of the abdominal walls, restoresthe former condition of things, and so the diaphragm is car-ried upward, and expiration results. When, however, the ex- 92 HUMAN PHYSIOLOGY. O
Human physiology : designed for colleges and the higher classes in schools and for general reading . as they occur in inspiration. It is supposed that inordinary expiration, there is little, if any, muscular action—that as the diaphragm, which in inspiration pushed down thestomach and liver, and thus thrust out the walls of the ab-domen, ceases to contract and relaxes, the mere elasticity ofthe parts below, and especially of the abdominal walls, restoresthe former condition of things, and so the diaphragm is car-ried upward, and expiration results. When, however, the ex- 92 HUMAN PHYSIOLOGY. Other muscles, besides the diaphragm, act in inspiration. piration is at all forcible, it is produced in part by tbe actionof the muscles of the abdomen and some of the muscles aboutthe chest. 136. While this dome-shaped muscle, the diaphragm, is theprincipal agent by which the chest is enlarged, there are othermuscles which do the same thing in another way. In Fig. 40,a is the spine; c, c, c, the ribs ; b, the breastbone ; d, the col-lar-bone ; g, the diaphragm. You observe, on the right side. c a h WALLS OF THE CHEST. of the chest, certain muscles, i, extending from the spinalcolumn in the neck to the first rib. When these contract, theeffect will be to raise this first rib, and all the others, beingattached to it, of course follow. And, as the ribs, as you seein Fig. 37, slant downwards from the spine toward the front,the result will be, that all the ribs will be carried together for-ward and upward. This result is the more effectually securedby muscles which pass from rib to rib, as seen at e, e, e, e. Inthis Figure, the ribs, c, c, c, are left bare on the left side, to show RESPIRATION. 93 Arrangement of muscles between the ribs. the arch of the diaphragm, ff, the dotted line indicating it onthe right side. 137. There are two layers of muscles connecting the ribs,the fibres of which cross each other, as represented at M, inFig. 41. R R are parts of two ribs. The spaces be
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