The wrist joint proper does not permit rotation since
it is a condyloid articulation, but pronation and supination
of the hand replace this movement of rotation. Prona-
tion and supination are the result of rotation of the radius
at the humero-radial joint, round an axis running down-
wards from the head of the radius through the styloid
process of the ulna and the metacarpal bone of the little
finger. In the practical application of pronation and su-
pination, as seen in the use of boring instruments, for in-
stance, there is another agent brought into play, and with-
out which, these movements would be very much limited,
and this agent is the shoulder joint. It will be noticed in
boring, etc., that, to supination is added adduction and
outward rotation of the humerus, while, to pronation there
is added abduction and inward rotation. This change of
position of the humerus, during supination and pronation
of the forearm, adds to the efficiency of these movements,
since it alters the situation of the base from which they


Wrist and Hand. IOI


proceed, viz., the lower end of the humerus, and thereby
increases the scope and strength of their application. With-
out these accessory actions of the humerus, the hand could
be supinated and pronated only through an angle of about
80°; with them, the range may reach in the neighborhood
of 340°.
