The Notebooks of Leonardo Da Vinci Volume 1

Excerpt: ...This extension and bending vary in manner; that is, sometimes they bend altogether at the first joint; sometimes they bend, or extend, half way, at the 2nd joint; and sometimes they bend in their whole length and in all the three joints at once. If the 2 first joints are hindered from bending, then the 3rd joint can be bent with greater ease than before; it can never bend of itself, if the other joints are free, unless all three joints are bent. Besides all these movements there are 4 other principal motions of which 2 are up and down, the two others from side to side; and each of these is effected by a single tendon. From these there follow an infinite number of other movements always effected by two tendons; one tendon ceasing to act, the other takes up the movement. The tendons are made thick inside the fingers and thin outside; and the tendons inside are attached to every joint but outside they are not. Footnote 26: This head line has, in the original, no text to follow. Of the strength and effect of the 3 tendons inside the fingers at the 3 joints. The movement of the torso (355-361). 355. Observe the altered position of the shoulder in all the movements of the arm, going up and down, inwards and outwards, to the back and to the front, and also in circular movements and any others. And do the same with reference to the neck, hands and feet and the breast above the lips &c. 356. Three are the principal muscles of the shoulder, that is b c d, and two are the lateral muscles which move it forward and backward, that is a o; a moves it forward, and o pulls it back; and bed raises it; a b c moves it upwards and forwards, and c d o upwards and backwards. Its own weight almost suffices to move it downwards. The muscle d acts with the muscle c when the arm moves forward; and in moving backward the muscle b acts with the muscle c. Footnote: See Pl. XXI. In the original the lettering has been written in ink upon the red chalk drawing and the outlines...