ARLBERG ([.a]rl´ber_h_), a branch of the Rhætian Alps, in the west of Tyrol, between it and Vorarlberg, pierced by the fourth longest railway tunnel in the world. It is 6½ miles long, and was finished in Nov., 1883, and connects the valley of the Inn with that of the Rhine, and the Austrian railway system with the Swiss railways.
AR´LECDON, an urban district of England, in Cumberland, 4 miles east of Whitehaven, with coal and iron mines. Pop. (1921), 5152.
ARLES ([.a]rl; ancient, AREL[=A]TE), a town of Southern France, department Bouches du Rhône, 17 miles south-east of Nismes. It was an important town at the time of Cæsar's invasion, and under the later emperors it became one of the most flourishing towns on the farther side of the Alps. It still possesses numerous ancient remains, of which the most conspicuous are those of a Roman amphitheatre, which accommodated 24,000 spectators. It has a considerable trade, manufactures of silk, &c., and furnishes a market for the surrounding country. Pop. 16,746.
AR´LINGTON, Henry Bennet, Earl of, member of the Cabal ministry, and one of the scheming creatures of Charles II, born 1618, died 1685. He is supposed to have lived and died a Roman Catholic.
AR´LON, a Belgian town, capital province of Luxemburg, a thriving town, with manufactures of ironware, leather, tobacco, &c. Pop. 12,012.
ARM, the upper limb in man, connected with the thorax or chest by means of the scapula or shoulder-blade, and the clavicle or collar-bone. It consists of three bones, the arm-bone (_hum[)e]rus_), and the two bones of the fore-arm (_radius_ and _ulna_), and it is connected with the bones of the hand by the _carpus_ or wrist. The head or upper end of the arm-bone fits into the hollow called the _glenoid cavity_ of the scapula, so as to form a joint of the ball-and-socket kind, allowing great freedom of movement to the limb. The lower end of the humerus is broadened out by a projection on both the outer and inner sides (the outer and inner _condyles_), and has a pulley-like surface for articulating with the fore-arm to form the elbow-joint. This joint somewhat resembles a hinge, allowing of movement only in one direction. The ulna is the inner of the two bones of the fore-arm. It is largest at the upper end, where it has two processes, the _coronoid_ and the _olecranon_, with a deep groove between to receive the humerus. The radius--the outer of the two bones--is small at the upper and expanded at the lower end, where it forms part of the wrist-joint. The muscles of the upper arm are either _flexors_ or _extensors_, the former serving to bend the arm, the latter to straighten it by means of the elbow-joint. The main flexor is the _biceps_, the large muscle which may be seen standing out in front of the arm when a weight is raised. The chief opposing muscle of the biceps is the _triceps_. The muscles of the fore-arm are, besides flexors and extensors, _pronators_ and _supinators_, the former turning the hand palm downwards, the latter turning it upwards. The same fundamental plan of structure exists in the limbs of all vertebrate animals.