ATTACHMENT OF THE MUSCLES TO THE BONES (p. 30).--One of the two bones to which a muscle is attached is usually less mobile than the other, so that when the muscle shortens, the latter is drawn down against the former. In such a case, the point of attachment of the muscle to the less mobile bone is called its origin, while the point to which it is fixed on the more mobile bone is called its attachment....A muscle is not always extended between two contiguous bones. Occasionally, passing over one bone it attaches itself to the next. This is the case with several muscles which, originating from the pelvic bone, pass across the upper thigh bone, and attach themselves to the lower thigh bone. In such cases the muscle is capable of two different movements: it can either stretch the knee, previously bent, so that the upper and the lower thigh bones are in a straight line; or it can raise the whole extended leg yet higher, and bring it nearer to the pelvis. But the points of origin and of attachment of muscles may exchange offices. When both legs stand firmly on the ground, the above-mentioned muscles are unable to raise the thigh; instead, on shortening, they draw down the pelvis, which now presents the more mobile point, and thus bend forward the whole upper part of the body. One important consequence of the attachment of the muscles to the bones is the extension thus effected. If the limb of a dead body is placed in the position which it ordinarily occupied during life, and if one end of a muscle is then separated from its point of attachment, it draws itself back, and becomes shorter. The same thing happens during life, as is observable in the operation of cutting the tendons, as practiced by surgeons to cure curvatures. The result being the same during life and after death this phenomenon is evidently due to the action of elasticity. It thus appears that the muscles are stretched by reason of their attachment to the skeleton, and that, on account of their elasticity, they are continually striving to shorten. Now, when several muscles are attached to one bone in such a way that they pull in opposite directions, the bone must assume a position in which the tension of all the muscles is balanced, and all these tensions must combine to press together the socketed parts with a certain force, thus evidently contributing to the strength of the socket connection....This balanced position of all the limbs, which thus depends on the elasticity of the muscles, may be observed during sleep, for then all active muscular action ceases. It will be observed that the limbs are then generally slightly bent, so that they form very obtuse angles to each other.