[Prehension of the human hand]

Only one of the many methods of grasping of the living beings, prehension assumes in many many functions: feeding, cleaning, making of tools and arms, working and hunting, environmental modifications, cultural and social activities, communication. Indeed, the hand is the irreplaceable organ of man of which seven degrees of freedom allow its positioning in relation to the object and carrying of food to the mouth. Prehension is achieved thanks to the thumb opposition against the four long fingers, many kinds of pinches with two or more fingers and many types of simple or complex grips; the most sophisticated is the "grip plus action", such as lighting up a lighter. The hand skeleton is composed of five osteo-articular chains for the four long fingers and the thumb which is shorter and more mobile. There are two categories of muscles: intrinsic muscles located in the hand, dedicated to precision and coordination actions, and extrinsic muscles in the forearm for strength and large range of motion, with long tendons sliding in sheaths. Three functions are ensured by muscles: three types of flexion of long fingers: regular flexion, intrinsic and extrinsic flexions, extension which needs balanced action of intrinsic and extrinsic muscles, opposition and counter-opposition of the thumb. The two surfaces of the hand are opposite in their function: the palmar surface is an surface "of strength", while the dorsal is one "of weakness". Hand command and control are very interesting notions.(ABSTRACT TRUNCATED AT 250 WORDS)