Special anatomy and histology: in two volumes (Volume 1).

  • Horner, William E. (William Edmonds), 1793-1853.
Date:
1851
Catalogue details

Licence: Public Domain Mark

Credit: Special anatomy and histology: in two volumes (Volume 1). Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    SECT. XI.—OF THE MECHANISM OF THE THORAX. The thorax performs two very important offices in the animal ma- chine ; the first is to contain and protect the organs of circulation and of respiration, the second to assist in the function of respiration and perhaps that of circulation.1 The mechanism of the thorax is such that the solidity of its materials, and its rounded shape, present a very efficacious defence of its viscera, from the influence of blows on its outside. The effects of the latter are also materially diminished by the thickness and contraction of the several larger muscles which are placed on its surface. On its back part the thick longitudinal muscles of the spine, as well as those run- ning to the superior extremities, fill up the gutters on each side of the spinous processes, and make a fleshy protuberance, divided into two by the raphe which extends the length of the back over the spinous pro- cesses. In front it is less protected, owing to the sternum being im- mediately under the skin. Nevertheless, when blows are inflicted on this part, their effects are much diminished by the elasticity of the cartilages of the ribs, and by the direction, obliquely downwards, of the ribs themselves; both of which dispose the sternum to retreat backwards, and to yield to the impelling force. The recession will take place more readily at the moment of expiration, and when the muscles which elevate the ribs are not on their guard. In those delibe- rate exertions of the strength of the thorax, exhibited by individuals lying down on their backs, and sustaining a heavy weight on the ster- num, the ribs are saved from injury by different means. The arched form, itself, of the front of the thorax, is of considerable service in the resistance under such circumstances; this, however, would be easily overcome, and the ribs would break, if the arch were not sustained in its elevation by the contraction of the large muscles on its sides, as the ser- ratus major, the pectoralis major and minor, each of which, by acting on the depressed anterior extremities of the ribs and their cartilages, has a tendency to keep them elevated. Fractures of the ribs, from blows or force applied in front, are not so liable to occur in the part stricken as in the point feeling the greatest momentum, which from the semi- circular form of the ribs is in or near their middle : this exhibits a true example of what the French writers call the contre-coup. Bichat says that the fracture by contre-coup is much more common when the individual, being struck unexpectedly, has not had time to throw his muscles into a state of contraction, for the protection of the ribs. The lateral convexity of the thorax being greater than that in front or behind, and having the same assistance from the muscles mentioned, presents a stronger resistance when blows are inflicted directly on it. Each rib represents an arch, the summit of which is its centre, and the base its two extremities. The abutments of the base are, the ster- num at one end and the spine at the other: a displacement from them is completely prevented by the strength of the ligamentous attach- 1 A very interesting paper on this subject was presented to the French Institute by M. Barry, some years ago.