Relations.—This muscle is covered by the external palmar aponeurosis, more internally by the tendun of the long flexor of the thumb, then by the common flexor tendons. It covers the first dorsal interosseous, the tendon of the radial flexor of the wrist, and a small portion of the external margin of the adductor of the thumb. Its outer edge corresponds to the abductor and is often confounded with the opponens, and its inner would be undistin guishable from the abductor near the first meta carpal bone, if it were not separated from it by the arteria magna pollicis,*—a fact that appears to have been overlooked by many anatomists, or the descriptions of the attachments of this muscle would never have been so much at variance ; the foregoing description coincides with that of Aleckel and Cruveilhier. Its tendon of insertion is covered by that of the abductor, which is external to it.
This muscle is badly named, at least if names be intended to denote action, for its power of flexing the thumb is very slight ; but it has considerable power as an opposer of it, its insertion being especially favourable to that action.
4. Adductor pollicis manes (metacarpo-pha langien da pouce, Chauss.) is the largest muscle of the thumb as well as the most internal ; in shape it is a perfect triangle, arising from all the anterior border of the third metacarpal bone, from its articulation with the magnum, from the anterior and superior portion of the trapezoid, and from the palmar interosscous aponeurosis in its central portion. From this extensive attachment the fibres run transversely utwards, the superior ones being most oblique; they converge to a strong fleshy bundle, which is inserted by means of the internal sesamoid bone into the first phalanx of the thumb.
Relations.—Its two internal thirds are covered by the himbricales and common flexor tendons, also by a layer of the deep interosseous apo neurosis which constitutes its sheath. It covers the two first interosseous spaces. Its inferior border is subcutaneous, especially posteriorly, where it may be felt in the fold of skin extend ing from the index finger to the thumb.* Its name implies its action ; it draws the thumb towards the median line of the hand.
b. Muscles of the internal palmar region.— There are four muscles in this region also; one is a cutaneous muscle, the pal maris brevis ; the others are proper to the little finger, and are inserted into the inner side of its first phalanx and the fifth metacarpal bone. They consist,
as the last described set, of an abductor, short flexor, and an opponens minimal digiti.
I. Palmaris brevis (pcancier de la main, Cruveilh.) This muscle when it exists, (for in weakly subjects its fibres are often not to be distinguished, though on the other hand it acquires considerable volume in those that are muscular,) arises by aponeurotic intermingled with fleshy fasciculi which run horizontally inwards, forming a small quadrilateral muscle which terminates in the skin.
Relations—Covered by the skin and im bedded in the adipose substance, it is spread over the muscles of the little finger and the ulnar artery and nerve, from which it is sepa rated by the internal palmar aponeurosis.
increases the concavity of the palm by puckering the skin over the part it occupies, thereby drawing the hypothenar eminence for wards and outwards, and rendering it more convex.
2. Abductor minimi digiti (pisi-phalangien, Cruveilh.) A long flat muscle, broadest at its centre, arising from the pisiform bone and from an expansion of the flexor carpi ulnaris, by strong aponeurotic fibres, which soon become fleshy, running along the inner edge of the fifth metacarpal bone. It ends in a flattened tendon, which is inserted in common with the short flexor into the inner side of the first phalanx, sending an expansion into the extensor tendon.
Relations.—It is covered by the internal palmar aponeurosis, itself covering the oppo nens.
Use.—It draws the little finger inwards and forwards, separating it from the others.
3. Flexor brevis minimi digiti (unci-phaturt gicn, Cruveilh.)—This muscle is external to the last ; it arises from a small portion of the annu lar ligament and from the anterior part of the unciform process ; it runs downwards and in wards to join the last described muscle, with which it is inserted.
Rclations.—At its origin it is separated from the abductor by the ulnar vessels and nerve, but it soon becomes confounded with it. Chaussier described them both as one muscle. It is often wanting. In concert with the last, it abducts and slightly flexes the little finger.
4. Adductor ossis metacarpi or opponens minimi digiti ( unci-metacarpicn, Cruvei I h .)—I t resembles in disposition and form the opponens pollicis. Having the same origins with the preceding muscle, its fibres proceed downwards and inwards, the superior being nearly hori zontal ; they are inserted into all the internal border of the fifth metacarpal bone.