These appliances are constructed in two ways; some are fixed to the end of the forearm and are immobile, some are attached by means of a joint or joints and are capable of rotation in various directions.
(a) Fixed Appliances.—We illustrate here an appliance derived from the simple hook, the vine-dresser's claw, devised some time ago by Gripouilleau; branches of varying size can be held while the other hand saws them or cuts them with the pruning shears (Figs. 163 and 164).
Fig. 163.—Vine dresser's hook. (Gripouilleau).
Fig. 164.—The branch is held in the grip by a leverage exerted by torsion.
This appliance of Gripouilleau, with a series of hooks, forms the basis of almost all the "pincer hands" constructed by M. Boureau and characterised by—
(1) The closure of the upper hook which is thus transformed into a ring, the two appliances being combined in one;
(2) The spring fixed to the straight side of the hook providing the grip necessary for holding articles. If the free end of the spring is turned up like the pointed toe of a mediæval shoe a sufficiently large opening is left between it and the straight edge of the hook to enable an object which is fixed mechanically or held by the other hand to be pushed into and gripped by the spring.