. A manual of diseases of the nervous system. , but do not move the fingers laterally. The oppositeaction of the forearm muscles and of the interosseous extensors and flexors is veiyimportant. Their synergic action steadies movements, and in many actions theycontract alternately. Thus in making a down-stroke with a pen or pencil thelong flexors bend the last two joints; while in making an up-stroke these areextended, and the metacarpo-phalangeal joint is flexed, by the interossei. Inparalysis of these muscles the lateral movements are lost, but a slight abductionand adduction of the index can
. A manual of diseases of the nervous system. , but do not move the fingers laterally. The oppositeaction of the forearm muscles and of the interosseous extensors and flexors is veiyimportant. Their synergic action steadies movements, and in many actions theycontract alternately. Thus in making a down-stroke with a pen or pencil thelong flexors bend the last two joints; while in making an up-stroke these areextended, and the metacarpo-phalangeal joint is flexed, by the interossei. Inparalysis of these muscles the lateral movements are lost, but a slight abductionand adduction of the index can still be effected by its long extensors. Only thefirst phalanx can be extended, and flexion is almost confined to the last twophalanges. The first two lumbricales, being supplied by the median nerve,often escape when the other muscles are paralysed by an injury to the ulnarnerve, and they aid the others when these are merely weak; hence the indexand middle fingers seem to recover before the others (Fig. 15). The position of Fia. 15. Fia. Fig. 15.—Recent incomplete paralvsis of the interossei from a puncturedwound of the uluiir nerve at the wrist: iittempt to extend fingers. The lossof extension of the last two phalanges is cliieHy marked in the third and fourthfingers, from the influence of the lumbricales (supplied by the median) on theothers. (After Duclienne.) Pig. 16.—\sis of the interossei (ulnar uerve) slight in degree: attitudeof fingers at rest. the hand at rest becomes altered. Normally there is slight flexion at all jointsby the tone of the muscles, interossei and long flexors. In paralysis the firstphalanx is in a line with the metacarpal bones, while the other phalanges areflexed, the middle more than the distal (Fig. 16). In action this flexion isalways increased, the metacarpo-phalangeal joints become over-extended, andthe other joints strongly flexed (Fig. 17). Gradually the hand assumes thisposture even at rest (Fig. 18), and ultimately the postur
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