THE RADIAL NERVE. 59] 
nerve varies in size, according to the bulk of the lesser internal cutaneous and 
intercosto-humeral nerves. 
2. Muscular branches (rr. musculares).—These are in two sets. One series supplies 
the long head of the triceps muscle near its origin; the 
other series enters the inner head of the muscle. One 
of the latter, separating itself from the rest, accompanies 
the ulnar nerve in the middle third of the arm, and 
supplies the lower part of the muscle. This is some- 
times called the collateral ulnar nerve. 
Branches arising on the back of the humerus.-— 
Muscular branches arise from the nerve in the musculo- 
spiral groove for the supply of all three heads of the 
triceps muscle. The branch which enters the inner 
head of the muscle, besides supplying it, passes through 
the muscle and behind the external condyle of the 
humerus, to terminate in the anconeus. 
Branches arising at the outer side of the 
humerus.—1. The cutaneous branches (n. cutaneus anti- 
brachn dorsalis) are two in number, superior and inferior. 
Arising from the musculo-spiral nerve before it pierces 
the external intermuscular septum, these branches 
pierce the deep fascia close together on the outer side 
of the arm in its lower half. Descending over the back 
of the external condyle, the superior branch supplies the 
skin of the outer side and back of the arm in its lower 
third, and the back of the forearm in its upper half. 
The inferior branch supphes an area of skin on the back 
of the forearm in the upper two-thirds internal to the 
area innervated by the musculo-cutaneous nerve (Fig. 
433, p. 588). 
%. Muscular branches.— The musculo-spiral nerve, as 
it hes in the interval between the brachialis anticus 
and brachio-radialis, supplies a small branch to the Fie. 435.—Dracrammatre Rerre- 
brachialis anticus (w hich msome cases is, not present) Sc coe No 
and nerves to the brachio-radials and extensor carpi 
M.S, Musculo-spiral nerve; L.H, 
radialis longior. It may also provide the nerve to the ‘Nerve to long head of triceps : 
3 
extensor car pl radialis brevior. 1.C, Internal cutaneous branch ; 
I.H, Nerve to inner head of 
triceps ; O.H, Nerve to outer head 
RADIAL NERVE. of triceps ; I.H, Second nerve to 
inner head of triceps; Ane, 
The radial nerve (1. superficialis) is entirely eae. peste oe a qe 
cutaneous in its distribution. Arising in the hollow of . external cutaneous branch - E.Ci, 
the elbow beneath the brachio-radialis, it courses down- Inferior _ external cutaneous 
wards under cover of that muscle through the upper re. a Nee pee 
two-thirds of the arm, and accompanies the radial artery  yadialis ; E.C.R.L, Nerve to ex- 
in the middle third of the forearm. It then passes _ tensor carpi radialis longior ; P.1, 
backwards beneath the tendon of the brachio-radialis Se ia a HENS 
and pierces the deep fascia in the outer side of the fore- ‘ 
arm in the lower third. It is distributed to the skin of the back of the wrist, 
the outer side and the back of the hand, and the back of the thumb and outer 
two and a half fingers (Fig. 435, p. 588). Its branches communicate on the ball 
of the thumb with the musculo-cutaneous nerve, and on the back of the hand with 
the dorsal branch of the ulnar nerve. The digital branches are small, and are five 
in number. Two pass to the back of the thumb and reach the inter-phalangeal 
articulation. One supplies the radial side of the index finger as far as the second 
phalanx. The remaining two branches divide at the clefts between the second and 
third, and third and fourth fingers respectively, and innervate the adjacent sides of 
these fingers as far as the second phalanx. The rest of the skin of these digits to 
the tips is supplied by digital branches of the median nerve. 
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