Note 101 — Chapter IX · OF THE INFLUENCE OF THE DEATH OF THE LUNGS, OVER THE GENERAL DEATH OF THE BODY.

When from any cause, the diaphragm cannot contract, the enlargement of the thorax is effected solely by the elevation of the ribs, and as this motion is then very evident, we can then appreciate better the influence the intercostal muscles have in its production in ordinary respiration. Haller, as is well known, supposed that the first rib was almost immoveable, and that the muscles in the first intercostal space, took it as their fixed point to elevate the second. This second rib, in its turn, served as a fixed point to elevate the third, and thus on to the last rib. But if we observe the mechanical phenomena of respiration when the diaphragm does not contract, as is the case in diaphragmatic pleurisy, we see that the first rib is far from being immoveable. Now, we cannot conceive how the intercostals which are attached to its inferior part, can, by contracting, assist in raising it. Besides, in order to elevate the ribs, a very great resistance must be overcome, and the intercostal muscles are too slender to induce us to suppose that they are capable of effecting it. The principal agents of this motion then are the anterior and posterior scaleni, which are distinctly seen to contract in great inspirations, the supra-costales and the muscles of the neck which attach it to the sternum. We ought to add to these a muscle, to which this use has never before been attributed; I mean the diaphragm. This muscle in fact in its contraction tends to become flat, from being concave as it is in inspiration. Now, its middle part in depressing the abdominal viscera experiences a certain resistance, and takes, as it were, from them a fixed point, by means of which it elevates the base of the thorax to which its circumference is attached.