THE DORSAL INTEGUMENT
Unlike the volar surface, the dorsal side of
the hand is covered with thin, soft, pliable
skin and equally mobile subcutaneous tissue,
both capable of yielding easily under tension.
Because in flexion of the fingers and in making
a fist the covering on the back of the hand must
be able to stretch from wrist to fingernails, the
dorsal skin is arranged in numerous minute
redundancies, which, in the fiat-of-hand, are
manifest in the typical transverse wrinkles,
particularly over the phalangeal articulations.
Special adaptations in the dorsal skin of the
thumb accommodate the distinctive rotational
planes of that digit about its carpometacarpal
articulation. In the normal, healthy
hand, the degree of redundancy in any given
area is just such that all wrinkles are dispatched
when the fist is clenched. Swelling in
any area, dorsal or volar, inhibits flexionextension
of the part affected.
NERVE AND BLOOD SUPPLY
Three principal nerves serve the muscles of
the hand (Fig. 9). Nerve supply is indicated,
except for minor variations and exceptions, in
Table 3. Each of these major nerve trunks
diverges into countless smaller branches ending
in the papillae of the palmar pads and dorsal
skin, and the whole neuromuscular system is
so coordinated in the brain that motor response
to stimuli is ordinarily subconscious and
reflex. Thus an object slipping from the grasp
is automatically gripped more firmly, but not
so firmly as to damage the hand itself. Noxious
stimuli are rejected automatically, as when