Essays and observations on natural history, anatomy, physiology, psychology, and geology / by John Hunter, being his posthumous papers on those subjects, arranged and revised, with notes ; to which are added the introductory lectures on the Hunterian collection of fossil remains delivered in the theatre of the Royal College of Surgeons of England, March 8th, 10th and 12th, 1855 / by Richard Owen.
- John Hunter
- Date:
- 1861
Licence: Public Domain Mark
Credit: Essays and observations on natural history, anatomy, physiology, psychology, and geology / by John Hunter, being his posthumous papers on those subjects, arranged and revised, with notes ; to which are added the introductory lectures on the Hunterian collection of fossil remains delivered in the theatre of the Royal College of Surgeons of England, March 8th, 10th and 12th, 1855 / by Richard Owen. Source: Wellcome Collection.
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![the older bone hollow. From this then we see that the greatest part of the bone is solid, and afterwards becomes hollow; therefore it is reasonable to think that the first ossification was solid, and then became hollow. The bones are such parts that do not grow or increase in any part while that part is exposed to the air; therefore Nature has taken care to cover bones that are sound as soon as possible [if they are by any accidental circumstance exposed]. Bones are commonly hard in proportion to their length; for, in pro- portion to their length they are obliged to make the greater resistance. Any lateral bias, wrench, blow, &c. more easily breaks a long bone than a short one. It in all cases acts with a longer lever. Animals whose bases of support and motion are formed of hard and solid parts, have them so joined as to allow of motion between them; which joints, in the formation of their parts, are so related to the appli- cation of the powers of motion, as to constitute what are called the mechanical powers or levers. A lever has the moving power, the centre of motion, and the resistance. And as these may be so placed with respect to each other as to vary their relative position as much as three numbers can, so are the joints in an animal variously formed. The joint of the foot upon the tibia is of all the three sorts. It is a lever of the first kind when we push anything with our toes; of the second kind when we raise anything with them; and of the third when we raise our body upon them. In mechanics, without resistance there could be no such thing as motion; but in animals, where there is a self-moving power, this can act without any resisting point. But this self-moving power cannot be applied to other parts, even in the animal, without a fixed point of resistance. However, these self-moving powers, by their simple action within themselves, may produce immediately the effect, without one point resisting more than another; as [in the instance of] a worm simply contracting and bringing its two ends together, or contracting laterally, so as to push itself out, by which means it is elongated; but even here the one half of the worm may be said to be the fixed point or point of resistance to the other; but a worm can fix any part of its body to whatever it lies upon, and move towards that point. A circular muscle would appear to have no fixed point, only the power of contrac- tion, or shortening itself; and from the figure the muscle is thrown into, it produces its effects; each portion becomes a fixed point to the other all round; therefore every moving body which acts mechanically, acts from some resisting power which may be called the fixed point, or centre of motion. But animals, more especially the compound ones,](https://iiif.wellcomecollection.org/image/b21182656_0406.jp2/full/800%2C/0/default.jpg)
