EXAMINATION OF SOME SPINAL NERVES 79 
An isolated field of response, that supplied by 8th cervical root, was finally delimited at 
4.30 p.m. This field was contained within the following boundary. From a point about one 
quarter the way up the outer edge of the upper arm, in the furrow between the biceps and triceps 
muscles, the boundary slopes abruptly back across the triceps for about 2 centims., and then 
recurves at less than a right angle to pass downward between the olecranon and the outer condyle 
of the humerus and gain the forearm. It descends the outer side of the extensor surface of the 
forearm for about one-third the way to the wrist, and then slants toward the ulnar side and attains 
the ulnar edge about one-third up the forearm. It slopes round as far as the flexor aspect of the 
ulnar edge and then sharply recurves on itself, tending upward and outward across the face of the 
flexor aspect of the forearm, to a point about two-fifths up the flexor aspect of the forearm, and 
midway between its radial and ulnar borders. Thence the line of boundary returns and descends 
just to the ulnar side of the pronator longus tendon. Close above the wrist it slopes outward 
and attains a point one centim. above the styloid process of the radius ; from that the line runs 
up the forearm on the outer face of the prominence caused by the prominence of the group of 
supinator muscles, and it ascends finally the furrow between biceps and triceps to the point 
whence it was originally traced.' 
The agreement between the limits of this field in the individuals observed has been 
singularly close ; the discrepancies have been too small to be clearly outside the limits of errors 
inherent in the experimental testing of the skin. The analogy between the cutaneous distribu- 
tion of the Vlllth cervical in the fore-limb, and of the Vlth lumbar (Vth lumbar of man) in the 
hind-limb, is curiously great. Each supplies the skin covering the whole free apex of the limb to 
which it belongs, and each has anterior to it a nerve-root which supplies the skin of only the 
anterior side of the free apex of the limb, and each has next behind it a nerve-root that supplies 
the skin of only the posterior portion of the free apex of the limb. 
Although this (Vlllth cervical) skin-field extends further along the radial edge of the fore- 
arm than along the ulnar edge, it was noted in each of the experiments made that when the 
' contracted field ' was examined, the reply from the pollex was much less brisk than from the fifth 
digit ; also, the reply from the radial side of the forearm was gradually developed under ' extension 
of the field.' The centre of the field in the hand lies, therefore, in all probability nearer to the 
ulnar than to the radial border. 
2. Motor Root. Vlllth cervical. {See Conspectus, p. 114 infra.) 
Three experiments, all on Macaais rhesus, and by combined degeneration and excitation 
method as above. 
The root is distributed to the following muscles : — - 
scaleni. 
pectoralis major, 
pectoralis minor. 
triceps (all three heads, especially, perhaps, to the long head). 
latissimus dorsi (especially to a portion near the humeral attachment). 
extensor carpi uinaris. 
