of
the radius, and in fracture of the neck of the bone. The deep branch may
be divided as it passes through the supinator in operations on old
fractures and dislocations in the region of the elbow. Division of the
superficial branch in the upper two-thirds of the forearm produces no
loss of sensibility; division in the lower third after the nerve has
become associated with branches from the musculo-cutaneous is followed
by a loss of sensibility on the radial side of the hand and thumb. Wounds
on the dorsal surface of the wrist and forearm are often followed by
loss of sensibility over a larger area, because the musculo-cutaneous
nerve is divided as well, and some of the fibres of the lower lateral
cutaneous branch of the radial.

[Illustration: FIG. 91.--To illustrate the Loss of Sensation produced by
Division of the Median Nerve. The area of complete cutaneous
insensibility is shaded black. The parts insensitive to light touch and
to intermediate degrees of temperature are enclosed within the dotted
line.

(After Head and Sherren.)]

#The Median Nerve# is most frequently injured in wounds made by broken
glass in the region of the wrist. It may also be injured in fractures of
the lower end of the humerus, in fractures of both bones of the forearm,
and as a result of pressure by splints. After _division at the elbow_,
there is impairment of mobility which affects the thumb, and to a less
extent the index finger: the terminal phalanx of the thumb cannot be
flexed owing to the paralysis of the flexor pollicis longus, and the
index can only be flexed at its metacarpo-phalangeal joint by the
interosseous muscles attached to it. Pronation of the forearm is feeble,
and is completed by the weight of the hand. After _division at the
wrist_, the abductor-opponens group of muscles and the two lateral
lumbricals only are affected; the abduction of the thumb can be feebly
imitated by the short extensor and the long abductor (ext. ossis
metacarpi pollicis), while opposition may be simulated by contraction of
the long flexor and the short abductor of the thumb; the paralysis of
the two medial lumbricals produces no symptoms that can be recognised.
It is important to remember that when the median nerve is divided at the
wrist, deep touch can be appreciated over the whole of the area
supplied by the nerve; the injury, therefore, is liable to be over
looked. If, however, the tendons are divided as well as the nerve, there
is insensi