FIG. 28.
Our hand is essentially a prehensile organ, and as such causes us to educate the flexors the most; the extensors, being mainly used to relax the grasp of the fingers, are weaker, and the constant strain spoken of above, being thrown upon them, explains the fact that in telegraph operating these are the muscles most frequently attacked by cramp. (See Symptomatology.)
The following figures are of interest as proving the great superiority, in point of strength, of the flexor over the extensor muscles of the wrist and fingers. The measurements were made by the dynamometer of V. Burq, great care being taken to apply the instrument upon corresponding points of the palmar and dorsal surfaces of the hand. The grasp of the average man, which includes all the flexor muscles of the fingers and thumb, equals 125 pounds, while the power of the flexors of the wrist, exclusive of the fingers, equals 40 pounds. In marked contradistinction to this the extensors of the wrist register 35 pounds, and the extensors of the fingers only 7. The total power of all the flexors is therefore 165 pounds, and that of the extensors 42 pounds, nearly four times less (3.92). In women the ratio is the same, although the number of pounds registered is about half.
From the foregoing enumeration of the muscles used in writing and telegraphing it may be seen that the brunt of the work does not fall on the same muscles in the two acts, so that operators are seen utterly unable to telegraph more than a few words intelligibly who can still write a fluent hand. The two forms of neuroses often coincide in the same subject, as all telegraphers are of necessity scriveners; in fact, the majority suffer from both forms, and as a rule the most difficulty is experienced in telegraphing, and not in writing, although the reverse is frequently seen. But rarely does one see an operator who, unaffected as far as telegraphing is concerned, has difficulty in writing on account of this curious neurosis.
Of the muscles enumerated in the foregoing discussion, six are supplied, either wholly or in part, by the ulnar nerve—namely, the first two interossei, adductor pollicis, flexor brevis pollicis (inner half), flexor carpi ulnaris, and flexor profundus digitorum (inner part); and seven by the median nerve wholly or in part—namely, the opponens and abductor pollicis, flexor brevis pollicis (outer half), flexor longus pollicis, flexor profundus digitorum (outer part), flexor carpi radialis, and flexor sublimis digitorum.
The remaining important muscles are supplied by the musculo-spiral and its branches, except the biceps, which is supplied by the musculo-cutaneous.
The ulnar nerve supplies fifteen of the muscles of the hand; many of these are not prominently brought forward in writing, but are more or less used in keeping the hand in the required position.
Poore, after a careful study of 32 cases of undoubted writers' cramp, found the muscles affected in the following proportions: