The _ligaments_ may be seen enfolding the finger-joints, and also crossing the wrist, underneath the _tendons_.
The muscles are compressed into _tendinous cords_ at their ends, by which they are _united to the bones_.
They are arranged in _pairs_, having reciprocal actions--each muscle having _a companion muscle_ by which the part which it moves is restored to its original position, when the influence of the first muscle is withdrawn, and the stimulus given to bring back the part.
Because muscles which lie _on the fore-arm_, and have their tendons fastened at the ends of the fingers, _contract_, and by becoming shorter, _draw the fingers upward_, and towards the arm.
[Verse: "Thou hast clothed me with skin and flesh, and hast fenced me with bones and sinews."--JOB XI.]
944. _Why can we throw back the fingers after they have been raised?_
Because the muscles at the back of the arm, _whose tendons are attached to the back of the fingers_, contract and restore them to their former position.
945. _What degree of strength do the muscles possess?_
The degree of strength of a muscle depends upon the _healthy condition_ of the muscle, the _amount of stimulus_ which it receives at the time of exertion, and the manner in which _its powers are applied_.
The great muscle of the calf of the leg has been found, when removed from a dead body, to be capable of sustaining a weight equal to _seven times the weight of the entire body_.
_But the contractile power of the living muscles_ is very great: the thigh bone has frequently been broken by muscular contractions in fits of epilepsy. And in cases where there has been a dislocation of the thigh, the head of the thigh-bone being thrown out of its socket, (Fig. 56) it has been found necessary to employ strong ropes, attached to a wheel turned by several hands, in order to _overcome the contraction of the excited muscles, and to enable the operator to restore the bone to its place_.
946. _What is the stimulus which sets the muscles in action?_
The muscles are excited to action by _the nerves_, which they receive from the _spinal cord_.
947. _Why does it require the influence of the will to set the arms in motion?_
Because the muscles which form their mechanism are _voluntary_ muscles--that is, they are subject to the _will of man_, and influenced by impulses directed to them through the nervous system _by the mind_, which is the governing power.