Figs. 152 to 154.
The fingers shown in [figures 155 to 157] are joined together into a single piece, which articulates with the metacarpal part of the hand upon a transverse axis.
They are held in a position of flexion at the metacarpo-phalangeal joints by four palmar springs and they are opened away from the thumb by the action of a cord which bifurcates from the thumb cord on the back of the hand. The pull of this cord is exerted upon the upper angle of a triangle from the lower border of which four cords pass on to the back of the phalanges. Figure 156 shows detail of a finger. We know that attempts have been made to isolate by surgical means the masses of the extensor and flexor muscles in the end of the stump, making from them little prominences, perforated with a tunnel which is lined with skin. The cords pass through the tunnels, and in this way are worked voluntarily. We are not sure that this is practicable.
Figs. 155 to 157.—Automatic fingers.
In figure 155 are seen the cavity in which the finger portion works and the axis upon which movement takes place, also the four palmar springs. In figure 157 the arrangement of the cords. In figure 158 the attachment of the spring to the finger. This pattern, which we have designed and which is not patented, seems to us to be simpler than those in which the interphalangeal joints are also articulated and are automatic. It gives a more accurate grip between the tips of the thumb and index finger.
The Brunet Grip.—The Brunet grip is described here because of its resemblance to the automatic thumb, both being worked on the same principles.
