ARLON, argon, Belgium, the capital of the province of Luxembourg, in the midst of the woods and mountain ridges of the Ar dennes. It is a thriving place, with manufac tures of ironware, leather, tobacco, earthen ware and clay pipes. It appears in the Antonine Itinerary, and from the coins, inscriptions and other antiquities found, must have possessed some importance even in the time of the Ro mans. It is mentioned under its present name in 870, in connection with the partitiori of Lor raine. It has suffered much in the various wars which swept across this part of Europe. From 1684 to 1697 it was in the hands of the French. It was ceded to Belgium in 1831. Pop. (1910) 12,012.
ARM, a term technically applied to that portion of the upper extremity of the body extending from the shoulder joint to the elbow, but popularly used to denote both arm and fore arm. The arm proper has one large and strong bone, the humerus, covered by strong muscles, which protect the blood vessels and nerves. The upper end of the humerus fits into the head of the scapula and with the clavicle forms the shoulder joint. The head of the humerus is held in the joint partly by ligaments, but mainly by the muscles attached to it. The motions of the arm are many. Those muscles that move the arm inward toward the chest are known as the abductors. These arc the pectoralis major, coraco brachialis, which also flex the arm, and the latissimus dorsi and teres major, which also extend the arm. The arm is moved away from the body by the deltoid, a large muscle on the outer side, and the supraspinatus, a smaller muscle going from the scapula. The arm is rotated outward by the infraspinatus and the teres minor, and rotated inward by the sub scapularis: All of these muscles arc fastened about the upper part of the humerus. The greater mass of the muscles of the arm are those that go to the forearm and that move that member. Those that flex the forearm, or bend the elbow, are the biceps, the brachiates and the brachio-radials, the former being the most important. It also aids in turning the forearm palm downward. The muscles that ex tend or stretch the forearm are the triceps and the anconeus. There are other movements of the forearm. The arm having two bones, the radius and ulna, one turns on the other and the movements of pronation and supination are produced. Pronation is accomplished by two muscles, the pronator teres and the pronator quadratus; the supinator makes the movement outward. The movements of flexion and ex tension take place in the elbow joint, which is hinged like those of pronation and supination, just below the elbow joint, the radius moving on the ulna. The union of the radius and ulna
with the bones of the wrist make a hinge-like joint, the wrist joint. Movements at the wrist are in four directions, flexion and extension, abduction and adduction. These movements, as well as those of the fingers, are made by a large group of muscles some 20 in number. There are in all 48 muscles concerned in the movements of the arm, forearm and hand. The blood supply of the arm is derived from the brachiocephalic of the right side and from the arch of the aorta on the left (see AORTA) in a single main trunk that divides at the bend of the elbow. The first portion is called the sub clavian and is not in the arm proper; the axillary, or second portion, begins at the outer border of the first rib and becomes the brachial just about the armpit where it may be felt and compressed. The brachial artery is the great trunk of the arm. It may be felt just inside the inner edge of the biceps muscle about the middle and there may be readily compressed in case of haemorrhage. At the bend of the elbow the brachial artery divides into the radial and ulnar, which supply the outer and inner sides of the forearm respectively. The radial artery is the one most frequently felt in deter mining the pulse; the ulnar may be used but as it lies deeper it is felt less easily. In the hand these arterial branches anastomose to form a superficial and a deep pahnar arch from which branches go to supply the fingers. Haemorrhages in the palm of the hand can be controlled there fore only by controlling both radial and ulnar arteries, or better by controlling the brachial just above the bifurcation in the elbow. This may be done by strongly flexing the forearm or by something held against the artery. The prin cipal veins of the forearm are the ulnar, the median and the radial; of the arm the cephalic and basilic. These empty into the axillary vein and this into the sub-clavian. The nerve sup ply of the arm is derived from the spinal cord from the fifth, sixth, seventh and eighth cervical, and the first, second and third thoracic nerves. These form a complex plexus, the brachial plexus. The main branches going to the differ ent muscles and supplying the skin areas are the median, ulnar, musculo spiral, musculo cutaneous and circumflex. Their distribution is exremely complex. See JOINT, DISEASES OF.