On the mechanism of respiration / by Francis Sibson, Esq.

  • Francis Sibson
Date:
1846
Catalogue details

Licence: Public Domain Mark

Credit: On the mechanism of respiration / by Francis Sibson, Esq. Source: Wellcome Collection.

    6/70 page 2
    Lateral muscles of locomotion (30). It may be affirmed that the numerous many-headed lateral muscles (30.30.30.) which pass from rib to rib, are devoted to locomotion. They, acting on alternate sides, draw the ribs to wffiich they are attached nearer to each other, curve the spine laterally, and spread the ribs of the opposite side farther apart. The other muscles probably serve both for locomotion and respiration. 4. The rihs are simple. The ribs of the Snake are so simple that their action in breathing is very intelli- gible. If we distend the lungs to the full, and note how the position of the ribs is changed, what muscles are shortened and what lengthened, we shall ascertain what movements of the ribs will cause an inspiration, what an expiration, and we shall discover what muscles are inspiratory, what expiratory. The shortening of a muscle is conclusive evidence of its action; if we find one set of muscles shortened when we distend the lungs, another set lengthened, we know that the shortened muscles are inspiratory, the lengthened expiratory. I have not ascertained expe- rimentally on the Snake that the same muscles act when the animal inspires that are shortened when we distend the lungs, but I have ascertained it in the Dog and the Ass. I observed these animals breathe when the muscles were exposed, noted the actions of the various muscles one by one, and after death inflated the lungs; those muscles that acted during inspiration were invariably shortened when the lung was distended, and those that were passive were lengthened; on the other hand, those muscles that were active during expiration, were shortened when the lungs were flaccid. This fact rendered it unnecessary to find out by further vivisec- tions the actions of the respiratory muscles, they could be ascertained leisurely on the dead body and represented by accurate drawings; such drawings I have made by aid of the tracing-frame recommended to me by Dr. Hodgkin*. These drawings exhibit the changes effected in the form of the chest, the direction of the ribs, and the length of the various respiratory muscles in inspiration and expiration. In the Snake all the ribs have similar motions and similar muscles by which the motions are effected. 5. On inspiration, or rather on distending the lungs, for I never noticed a snake inspire, the ribs are raised at their free extremity and throughout their whole course. The range of motion of the free end is greatest, that end being most remote from the centre of the ribs motion at the vertebrae. If we assume that the rib is a straight rod, we can examine the motions of the various ribs in relation to each other uncom- plicated by disturbing or diagonal motions. * This tracing-frame I have described in a paper on the Relative Situation of the Internal Organs, published in the volume for 1844 of the Transactions of the Provincial Medical and Surgical Association. It has been of essential value to me both in this inquiry and in that just referred to.
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