ARM, the human upper limb from the shoulder to the wrist, and the fore limb of an animal. (See ANATOMY : Superficial and Artistic, and SKELETON : Appendicular.) The word is also used of any projecting limb, as of a crane, or balance, of a branch of a tree, and so, in a transferred sense, of the branch of a river or a nerve. Arm in military language is a branch of the army whose primary duty is to fight, e.g., infantry, artillery, used in con tradistinction to a "service" whose duty is to supply or aid the fighting troops. In the plural, the word is applied to the sol dier's weapons. "Arms" or "armorial bearings" are the heraldic devices displayed by knights in battle on the defensive armour or embroidered on the surcoat worn over the armour and hence called "coats of arms." These became hereditary and are borne by families; similar insignia are used by nations, cities, episcopal sees and corporations generally. (See HERALDRY.)