Fig. 3. Section through radius, lunate, capitate, and the bony structure
of digit III, showing virtual centers of rotation of each segment upon the
next more proximal one. When the fist is clenched, the prominence of the
knuckles is formed by the head of the more proximal member of each articulation.
For nomenclature, see Table 1.
(Table 2) lie in the forearm and, narrowing
into tendons, traverse the wrist to reach insertions
in the bony or ligamentous components
of the hand. Generally, the flexors
(Fig. 4) arise from the medial epicondyle of
the humerus, or from adjacent and volar aspects
of the radius and ulna, and then course
down the inside of the forearm.
They are, therefore, in
part supinators of the forearm
(Fig.5).The extensors (Fig.6)
of wrist and digits originate
from the lateral epicondyle
and parts of the ulna, pass
down the dorsal side of the
forearm, and thus assist in
pronation. The thumb shares
in the general flexor-extensor
scheme, but its extensors and
abductors originate from midand
distal parts of radius and
ulna.