HAND, MUSCLES OF TILE. (Human Anatomy.) The varied and beautiful move ments of which the hand is capable are effected by muscles belonging to separate and distinct regions,—namely, one set of muscles which are the proper and intrinsic muscles of the hand itself, and a second set, which are continued into the dorsal or palmar region of the hand from the posterior or anterior surface of the fore-arm. In the present article it is proposed to describe the intrinsic muscles of the band ; but in con sidering the actions of that member or of any of its segments, it will be necessary to notice how far the second set of muscles contribute to or aid in their production.
The proper or intrinsic muscles of the hand may be divided into-1, those on the palmar; 2, those on the dorsal surface.
I. The muscles of the palm are fifteen in all. For convenience of description they may be classified into, a, those of the thumb, or external palmar region, constituting the thenar eminence; b, those of the little finger, or in ternal palmar region, forming the hypothenar eminence; c, those that occupy the hollow of — the hand, or the middle palmar region.
a. Muscles of the external palmar region, The muscles of this region, all of which belong to the thumb, are four.
1. Abductor pallicis menus• ( scaphoido phalangien, Cruveilh.) short, flat, broader above than below ; it arises from the anterior surface of the scaphoid and trapezium, the superior, anterior, and external part of the anterior annu lar ligament, and generally from a prolongation of the tendon of the extensor ossis metacarpi, by aponeurotic and fleshy fibres. It proceeds outwards and downwards to be inserted into the outer edge of the upper extremity of the first phalanx of the thumb. Sometimes the two origins of this muscle are not incorporated for some distance, giving the appearance of two muscles.
Relations.—It is covered by the skin and external palmar aponeurosis. It covers the opponens, a few fibres of which appear to its radial side, running in a transverse direction.
It is separated by a thin cellular line from the short flexor, which is on the same plane.
The obvious action of this muscle is to draw the thumb forwards and inwards, thus sepa rating it from the fingers.
2. Flexor ossis metacarpi, or oppanens polli cis (trapezo-mctacatpien, Cruveilh.), of a rhomboidal form ; it arises from the trapezium, and from the fore part of the anterior annular ligament, anterior to the sheath for the radial flexor of the wrist, by long aponeurotic fibres ; and posteriorly from a septum between it and the short flexor. From these attachments the fleshy fibres radiate downwards and outwards, being so much the shorter the higher and the more transverse they are. They terminate by short aponeuroscs along all the outer edge of the first metacarpal bone.
Relations.—With the exception of a small portion of its external border, this muscle is covered anteriorly by the preceding muscle. It covers the anterior surface of the first meta carpal bone, and its articulation with the tra pezium.
It draws the thumb inwards, turning it upon its own axis, so that it opposes its palmar aspect to the other fingers.
3. Flexor brevis pollicis manes (trapezo phalangimi, Cruveilh.) is a larger muscle than the two preceding ones, triangular, bifid supe riorly, having its anterior surface channelled ; arises by aponeurotic and fleshy fibres, exter nally from the Ibre and under part of the annular ligament, and from the process of the trapezium, internally and posteriorly from all the reflected portion of the annular ligament, forming the sheath for the radial flexor and extending to the os magnum, and from the os magnum often by a distinct portion. From these various origins the fleshy fibres run downwards and outwards, are more oblique as they are more internal, and terminate in a strong fleshy bundle which is attached to the external sesa moid bone and outer side of the first phalanx.