| Interossei | (supplied by the ulnar nerve) | 18 times. |
| Extensors of the thumb | (supplied by the musculo-spiral) | 10 times. |
| Flexor brevis pollicis | (supplied by the median and ulnar) | 7 times. |
| Abductor pollicis | (supplied by the median) | 7 times. |
| Flexor longus pollicis | (supplied by the median) | 4 times. |
| Adductor pollicis | (supplied by the ulnar) | 3 times. |
| Opponens pollicis | (supplied by the median) | 2 times. |
| All the muscles of the forearm, more or less, | 2 times. | |
—showing that the muscles supplied by the ulnar nerve were affected more often than those supplied by the others.
The musculo-spiral and its branches supply the extensors of the thumb, fingers, and wrist, besides the two supinators; and by referring to the muscles most called into action in the act of telegraphing it will be seen that the majority are supplied by this nerve and by the median, which supplies the majority of the flexors. This statement explains to a great extent the fact that telegraph operators may be unable to telegraph and yet be able to write, as the muscles most important in the two acts have not the same nerve-supply.
The integrity of these nerves is therefore of the first importance in all cases requiring the use of the fingers and forearm, and many cases of copodyscinesia undoubtedly have a subacute inflammation of these nerves, or at least a congestion of the same, as their foundation, the neuritis or congestion being overlooked, owing to its mild type.
S. Weir Mitchell12 states that subacute neuritis is often incapable of distinct clinical discrimination when of a mild type and when there is an absence of traumatic cause. Mills13 states that “a lesion of the sensitive fibres profoundly affecting this power of conducting impressions may not cause pain, and that pain is not a necessary symptom of inflammation of a mixed nerve: this is an important fact, as I think too much stress is often laid on pain as a symptom of neuritis, leading to error in diagnosis and treatment.”
12 Injuries of Nerves, and their Consequences, by S. Weir Mitchell, M.D., Philada., 1872.
13 F. T. Mills, M.D., “On Two Cases of Neuritis of the Ulnar Nerve,” Maryland Med. Journ., vol. viii. p. 193, 1881.
Other Forms of Copodyscinesia.—In violin-playing the bow is held steadily between the fingers and thumb for long periods at a time, and the left arm is forcibly held in supination in order to bring the fingers upon the strings—actions well calculated to cause trouble if persisted in, not taking into account the rapid movements of the fingers which are necessitated in playing and the movements of the arm in bowing. The violinist is therefore liable to suffer in both arms, but in a different manner in each, as different muscles are used in bowing and in fingering.
The other musical instruments necessitating great education in the movements of the fingers and wrist are also liable to cause these neuroses, but this is not true of those wind instruments which require education of the movements of the lips and tongue. Piano-playing is a frequent cause of these troubles, which have been known to appear quite suddenly during the practising of some difficult piece.
In fact, all occupations which require a muscle or a group of muscles to be kept in a constant more or less firm contraction, together with fine movements of co-ordination in themselves and in the neighboring muscles, may be expected to furnish cases of this class of disease; the muscles affected necessarily varying with the work done, mere routine work being more liable to cause trouble than that which is new and original, as in the latter case time has to be taken to elaborate it, thus giving temporary rest to the muscles.