EXAMINATION OF SOME SPINAL NERVES 115 
musculature of the forearm also. Indeed in the Cat it is often absent from the musculature of 
the hand itself. In Man it appears, as in the Cat, to be sometimes wanting altogether from the 
musculature of the limb, although not unfrequently it undoubtedly does contribute to it, then 
probably, as in the other types, occurring chiefly in the hand and flexors of the forearm. It is 
clear that, broadly described, the musculature of the fore-limb is built up by successive 
contributions of segments, which reviewed in series passing from the segmentally anterior to the 
segmentally posterior, first extend stepwise down the deltoid scapular group, including in that the 
clavicular part of pectoralis major. That the next step takes in the biceps and brachialis anticus 
and part of supinator longus, and tlie descent then follows down the radial side especially, until 
with the Vlllth cervical ray the whole length of the musculature of the limb is reached even to 
its extreme apex. The length of the limb thus having been attained, and occupied by 
successively longer and longer out-thrusts of four segments (just as I have described for the hind- 
limb), a number of other segments, usually two (Dog, Macacm\ thrust out each a process, which 
extends along the back of the process of the segment immediately anterior to it, and throughout 
the whole length of the limb. These segments are so intimately fused in the hand region that it 
is difficult to pick out from the rest any one muscle which shows more of this or that constituent. 
But in the forearm and arm it is less difficult ; thus, in the former, the extensor communis 
digitorum receives a root which does not contribute to either of the long flexores digitorum, and 
the latter often receive a root which never contributes to the long extensor digitorum ; in the arm 
triceps receives supply from two roots which never supply the biceps, the latter from one root 
which never supplies the triceps. 
Thor<%CK 
.rd 
Number of spinal 
nerve-root . . /. 
Shoulder . 
Elbow 
th 
Wrist. 
Fingers 
— \ Skin 
MUSCI : 
— j (exC^nsion) 
>r<t 
Shm 
Skin . 
Musa 3. 
(f/eA/'on). 
(extena/oni 
Afusc/e 
Skirv. 
(exCi 'ns/on). 
Conspectus of segmental range of spinal innervation of the skin and muscles covering and 
moved by and moving the joints of the upper limb. The sensory innervation of the 
deep structures may be looked upon as similar (see p. 94 supra) in segmental range to the 
motor innervation of the muscles. (See text, pp. 117, 1 18.) 
