The movements of the fingers principally consist in extending and
bending them. 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 of the
figures have in most places been inked over.]
357.