[13] Hands are nearly always made of lime wood, which has the advantage of lightness, but the fingers are fragile and easily break. Instead of using hornbeam, which is hard but heavy, as the fragility only affects the fingers, some makers have overcome this difficulty by reinforcing the fingers by what they call a "philippeau." The finger is divided throughout its whole length by a mortise 1·5 millimetres in width, in which are glued two layers of veneering wood (mahogany, rosewood, etc., extremely hard woods, or else a layer of hornbeam). It may be a simple show hand without any joint. This pattern is no longer used. It may be jointed in one or in several fingers. We shall first consider certain principles of construction which we can explain by describing the chief mechanisms used. _Simple Spring Grip Thumb._--The simplest and most useful articulation is that of the thumb, which when at rest is kept by means of a spring in the flexed position, with the grip against the index finger which is partly flexed (as are also the other fingers). In many cases the patient is content with this simple mechanism. He opens the spring with the other hand and allows it to close on the object he wishes to grip (Figs. 139-145). [Illustration: FIGS. 139 to 142.--_Mechanism of the passive spring thumb._ The thumb turns on the axle D upon a piece which fits by a tapered extremity C into a hollow cut out in the thenar eminence. The base of the thumb is rounded. The spring AB flexes the thumb.] [Illustration: Figs. 143 to 145.--The Beaufort Thumb. The model shown on page 98 is more mobile than this, in which the thumb turns on the axis AB, and is fitted directly into the thenar eminence. But in this type it will be seen that the spring CD which keeps the thumb flexed, reaches right up to the wrist, and is therefore longer and more powerful. The thumb is much stronger, and this is the mechanism usually adopted. It has the inconvenience that it requires a deep excavation of the thenar eminence, encroaching upon the root of the index finger, so that it is impossible to mount the thumb in this way when it is desired to fit a movable metacarpo-phalangeal joint to the index finger, either with a spring (Fig. 155) or without (Fig. 148).] _The Automatic Thumb._--Active opening movement can be produced by the mechanism shown in figure 146. A cord fixed behind the scapula of the opposite side by a ring which passes over the clavicle and under the axilla, extends down the posterior surface of the arm and forearm pieces, running in pulleys which keep it in place. If the patient bends the elbow and at the same time brings the arm and both shoulders forward, rounding his back, the cord is tightened and pulls the thumb into the position of abduction and extension.