On account of this moveability of the two extreme middle-hand bones, it is possible to move the two edges of the hand close to one another, whereby the cavity of the hand assumes the shape of a groove.
The structure here described (the hand, in the narrower sense of the word) is joined to the lower arm by means of three muscles, the posterior row of the bones of the wrist (Fig. 1 c). The movement between these bones and the hand is hardly anything but a hinge-movement; that between them and the lower arm, however, is a movement in almost all directions. The bending and stretching of the hand is, therefore, produced with the participation of both joints, the side movement of the hand, however, almost exclusively by the joint situated between the posterior row of the bones of the wrist and the lower arm.[2]
2. Ligaments.
All the finger-joints are provided with capsules, which are woven out of strong transversal fibres (Fig. 3 aa). The bones of the wrist are connected between themselves and with the bones of the middle-hand by tight transversal and longitudinal ligaments, as seen in Fig. 2 aa, bb. Lastly, the two ends of the middle-hand bones, or knuckles, are connected with one another and with the first joints of the fingers by a separate strong, transversal ligament (Fig. 2 aa, Fig. 3 bb).
3. The Muscles of the Hand consist
1. Of muscles (four in number) rising from the lower arm and bending the wrist up and down, right and left (Fig. 3 c, d, e).
2. Of muscles of the fingers. These are subdivided into—
a. Extensors of the fingers, being situated in the back part of the hand and rising from the bones of the lower arm (Fig. 4 a).
b. Benders of the fingers. Two muscles, the one for the second joints of the fingers (Fig. 3 d), the other for the first joints of the fingers and the joints of the nails (Fig. 3 e) also rising from the bones of the lower arm.
