IIAND, BONES OF THE, (Human Ana tomy.) The hand (vie, maims; Fr. !amain; Germ. die lland,) is the inferior segment of the upper extremity. Its presence is charac teristic of man and the Quadrumana.
Although formed on the same general type, the hand will be found to exhibit many points of difference from the foot—characters strongly indicative of the diversity of use for which it is designed. In examining the skeleton of the hand, we observe subdivisions analogous to those which exist in the foot—the carpus cor responding to the tarsus, the metacarpus to the metatarsus, and the phalanges of the fingers in every way analogous to those of the toes. Independently of the lightness and mobility which are such prominent features in the me chanism of the hand, when contrasted with that of the foot, the divergence of the first or radial linger (the thumb) from the line of direction of the other four, is peculiarly cha racteristic of the hand. Whilst the four fingers, properly so called, are parallel to the middle line of the hand, the thumb, when extended, forms with it an angle of rather more than To this position of the thumb is due in the greatest part the facility of opposing it to one of the lingers, a movement so necessary in the pre hension of minute objects" The general form of the hand is oval, the obtuse extremity corresponding to the tips of the fingers, the unequal lengths of which oc casion the curvature in this situation. On its posterior surface or darsum, the hand is convex; on its anterior surface or palm, it is concave : both these surfaces correspond to, and in the recent state are supported by, the bones of the carpus and metacarpus.
I. Carpus (Germ. die Hatuiwurzel). The carpus bears a much less proportion in size to the whole hand than the tarsus does to the foot; it forms scarcely more than one-fourth of the hand. Its outline is oval, the long axis being transverse: if examined in a hand to which the ligaments are attached, the carpus will be found to form the posterior and osseous portion of an osseo-ligamentous ring, which gives pas sage to the tendons of the fingers. It is con
sequently hollowed from side to side, and is bounded on each side by a bony ridge, which gives attachment to the ligament (annular ligament) which forms the anterior part of the ring ; on the radial side the ridge is formed by a process of the os trapezium and of the sea phoid ; on the ulnar, where there is a more prominent ridge, by a process of the uncifurtn bone, and by the os pisifonne.
Seven bones, arranged in two rows, form the carpus. The superior row consists of the Os naviculare, os lunare, and os eunefforme, to which last is articulated a bone, constantly reckoned as a carpal bone, but which, I con ceive, may be more correctly regarded as a sesamoid bone, the as pisiforme. The second or inferior row is formed by the os trapezium, vs irapezvidcs,os magnum, and os unciArme.
1. Os navieulare (os seaphoideum ; Fr. le scaphoide; Germ. this &Wein). The na vicular or scaphoid is the largest of the upper row, and likewise the most external. Its su perior surface is convex, oval, with long axis transverse, articular, and is adapted to the outer part of the carpal articular extremity of the radius. The hollowed surface, to which it owes its name ( boat-like), is directed down wards and inwards; this is likewise articular and receives the head of the os magnum: con tinuous with and to the inner side of this hollow surface, there is a plane one of a semi lunar form, with which the os lunare is articu lated. The scaphoid bone articulates with the trapezium and trapezoides, by a convex surface directed downwards and outwards. Externally this hone terminates in a pointed extremity which receives the external lateral ligament of the wrist-joint and the annular ligament ( tuber mho; ossisnavicularis,s.enainentia carpi radialis superior). The anterior and posterior surfaces of the bone are rough, and give attachment to the anterior and posterior radio-carpal ligaments.