. A manual of diseases of the nervous system. not move the fingers laterally. The opposite action of the fore-arm muscles and of the interosseal extensors and flexors is veiy synergic action steadies movements, and in many actions they contractalternately. Thus in making a down-stroke with a pen or pencil the longflexors bend the last two joints; while in making an upstroke these are ex-tended, and the metacarpo-phalangeal joint is flexed, by the interossei. In para-lysis of these muscles the lateral movements are lost, but a slight abductionand adduction of the index can still
. A manual of diseases of the nervous system. not move the fingers laterally. The opposite action of the fore-arm muscles and of the interosseal extensors and flexors is veiy synergic action steadies movements, and in many actions they contractalternately. Thus in making a down-stroke with a pen or pencil the longflexors bend the last two joints; while in making an upstroke these are ex-tended, and the metacarpo-phalangeal joint is flexed, by the interossei. In para-lysis 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 three 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 aie merely weak; hence the indexand middle fingers seem to recover before the others (Fig. 15). The position of Fig. 15. Fia. 16. on. Fig. 15.—Recent incomplete paralysis of the interossei from a puncturedwound of the ulnar nerve at the wrist: attempt to extend fingers. The lossof extension of the last two phalanges is chiefly marked in the third and fourthfingers, from the influence of the lumbricales (supplied by the median) on theothers. (After Duchenne.) Fig. 16.—Paralysis of the interossei (ulnar nerve) 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 first 36 ACTION AND PAEALYSIS OF MUSCLES. phalanx 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 this Fig. 17. Fia. 18.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnervoussystem, bookye
