The hand : its mechanism and vital endowments, as evincing design / by Charles Bell.

  • Charles Bell
Date:
1860
Catalogue details

Licence: Public Domain Mark

Credit: The hand : its mechanism and vital endowments, as evincing design / by Charles Bell. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    and even granite would not be capable of sustaining four times the weight which the soft stone bore in the first instance. In the same way, the stones which form an arch, of a large span, must be of the hardest granite, or their own weight will crush them. The same principle is applicable to the bones of ani- mals : the material of bone is too soft to admit of an indefinite increase of weight. It is another illustration of what was before stated, that a relation is established through all nature; that the structure of the very animals which move upon the surface of the earth is proportioned to its magnitude, and the gravitation to its centre.] OF THE JOINTS. With regard to the articulation of the bones at the joints, we cannot mistake the reason why the surfaces of contact should be enlarged; the expansion of the ends of the bones makes them sit more securely upon each other, thereby diminishing the danger of dislocation. And this advantage is gained with- out detriment to the motion of the joint. In machinery, when the weight or pressure are the same, an increase in the extent of the surfaces in contact does not add to the friction. For example, if a stone, or piece of timber, of the shape of a book or a brick, be laid upon a flat surface, and drawn across it, it will be moved with equal facility whether it rest upon its edge, or upon its side. In the same manner, the friction be- tween the articular surfaces of the bones of the knee-joint, is not increased by their greater diameter; while obvious advan- tages result from their additional breadth : the ligaments knit the bones more strongly; and the tendons being removed to a distance from the centre of motion, more power is given to the action of the muscles. [In comparing the skeleton with carpentry, or with anything artificial that may admit of comparison with it, we remark an absence of straight lines or regular forms in the various bones, whether they serve the purposes of shafts, axles, or levers; while, in the mechanism made by man, every part is levelled and squared, or formed according to some geometrical line or curve. This, as. we have said, leads the superficial thinker to conclude, that the bones are formed irregularly, or without reference to principle. But the consideration of by Whom