. A manual of diseases of the nervous system. extensor of the metacarpalbone of the thumb, as may be noted if the finger is placed on the tendon beneaththe styloid process of the ulna. Hence, in paralysis of this extensor, the handdeviates laterally when the thumb is strongly extended. Extensors of the Fingers.—Extensor communis digitorum; E. indicis ;E. minimi digiti (musculo-spiral nerve—C. 6 and 7). The common extensormoves the fingers and then the wrist. When the muscle is faradised, theextension begins at the distal phalanges, and these become flexed again, whenthe hand is extended beyond
. A manual of diseases of the nervous system. extensor of the metacarpalbone of the thumb, as may be noted if the finger is placed on the tendon beneaththe styloid process of the ulna. Hence, in paralysis of this extensor, the handdeviates laterally when the thumb is strongly extended. Extensors of the Fingers.—Extensor communis digitorum; E. indicis ;E. minimi digiti (musculo-spiral nerve—C. 6 and 7). The common extensormoves the fingers and then the wrist. When the muscle is faradised, theextension begins at the distal phalanges, and these become flexed again, whenthe hand is extended beyond the plane of the forearm, by the tonic force of theflexors, the course of their tendons being elongated by the extension of the the muscle has little action on the last two phalanges, since theycannot be extended by the long extensor, if the interossei, their proper extensors,are paralysed. During extension by the communis the fingers are separatedfrom the second. The extensors of the first and last fingers have a similar. MUSCLES OP UPPER LIMB. 41 extensor action, but, in addition, they adduct their respective fingers towards themiddle finger. In paralysis, the extension of the fingers is impossible; but ifthe proximal phalanges are passively extended,the middle and distal joints canbe extended by the interossei. For the lateral movements of the digits, exten-Bion of the proximal phalanges is essential, and hence these movements arelost, but they can be performed if the proximal phalanges are passively posture of the fingers due to contraction of the palmar fascia resemblesthat in palsy of the long extensor (see Fig. 13), but an examination of thepalm shows the cause of the flexion. Flexors of Fingers.—F. sublimis (median nerve—all fibres C 7 and 8); (median and ulnar nerves). These muscles flex chiefly the secondand third phalanges, the first phalanx being flexed by the interossei. Thesuperficial muscle flexes the second phalan
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