The fingers are, of course, moved by a set of tendons, and the muscles, from which these tendons spring, are attached to the fore-arm (I purposely omit the scientific titles, though they would be much easier to write). Any of my readers can prove this for themselves.
Let him first grasp the upper arm firmly, and bend the limbs, and he will at once find that the swelling of the muscle shows the source of power.
Then let him do the same, but grasp the fore-arm, and he will find that the muscles are quiescent, showing that the former set of muscles belong to the entire arm, and not to the fingers, while the muscles of the lower arm have nothing to do with the bending of that limb.
Now let him grasp the fore-arm, and open and close the fingers, and he will feel a whole set of muscles rise, and swell and harden under his grasp. Next let him bend his hand inwards, and he will find that the fingers work perfectly well, though the direction of force is changed.
This is owing to a band of tendons passing across the wrist, under which the finger-tendons play. The course of the tendons is marked in the illustration by leaving them white.
The wondrous structure of the human hand and its multitudinous tendons can only be appreciated by actual dissection, but an idea of their variety and use may be obtained by watching the hands of a skilful pianoforte-player. This struck me forcibly the first time that I ever heard Thalberg play.
While on the subject of tendons, I may mention a curious case. A journeyman carpenter missed a blow with his axe, and struck his left hand at the junction of the thumb and wrist. The important tendon was severed, and the inner muscles, having no counteracting force, dragged the thumb into the hollow of the hand.
To all appearance, the man could no longer earn a living as a carpenter. But he would not be discouraged, and while he was in hospital he borrowed a book, and studied the anatomy of the human hand. By means of this knowledge he constructed a sort of semi-glove, in which he introduced pieces of watch-spring, that supplied the place of the lost tendon.
Not content with this, he studied Euclid for the purposes of his trade, so as to get the most possible out of a piece of wood of given dimensions, and be able to go straight to his mark by a problem, instead of doing it slowly and clumsily with a two-foot rule and a pair of compasses. When I saw him last he was a master carpenter in a large and increasing business.
Man has unconsciously imitated Nature in the invention of the Pulley, whereby the direction of force may be altered almost at will. In this case the cord takes the part of the working tendon, and the Pulley of the fixed tendinous crossbar. There is much matter of interest in the tendons, but, as our space is fast waning, I must resist the temptation of describing them.