ARLT, FERDINAND, Ritter von (1812-87). An Austrian oculist, born near Teplitz. He studied medicine at Prague and was professor of diseases of the eye there from 1849 to 1856, when he was appointed to a similar chair at the Uni versity of Vienna. Arlt was the author of a number of works on the eye and its diseases, in cluding Die Pflege der Augen inn gesunden and kranken Zustande (Prague, 1846, and subse quent editions) : licher die Ursaehen nod die Entstehang der Kurz..sichtigkeit (Vienna, 1876), a number of memoirs in the Archiv ffir Ophthalmologie, of which he was one of the editors, etc. His hest-known work is Die Krank heiten des Auges fiir praktische Aerzte geschildert (ed. 1, 3 vols., Prague, 1851-50), which passed through several editions. Consult his autobi ography (Wiesbaden, 1887).
ARM (Lat. neut. plur. arma, arms, weapons). A weapon of any kind; also used to designate a branch of the military service: as, the cavalry arm, the infantry arm, etc. It has, in addition, a wide application in naval and military termin ology to express the end, or branch, of any thing, particularly of articles or objects that have two similar ends, as yard arms, axle-tree arms (gun carriage), anchor arms, etc. See ARTILLERY ; ORDNANCE; SMALL ARMS; SWORDS, and other weapons.
ARM (Ger., Dan., Swed., and Dutch arm, A. S. earm, army, Cloth. arms. Lat. armas, the shoulder, Gk. cipp6e, harnios, shoulder-joint, all from the Indo-European root or, to fit, join). The upper extremity of the human body. It consists of two po•tions—the arm, strictly so called, and the forearm; the former having one bone, the humerus, which moves freely by a globular head upon the scapula, forming the shoulder-joint; and the latter having two bones, the radius and ulna, which move on the lower end of the humerus, forming the elbow-joint, and below, with the carpus, forming the wrist.
The humerus is attached by a loose capsular ligament to the scapula, allowing great freedom of motion, and were it not for the muscles would be frequently dislocated, but it is sup ported by muscles on all sides except underneath or opposite the armpit, in which direction the head of the bone is often driven by violence. The roundness of the shoulder is due to the head of the humerus, so that any displacement is ac companied by a flattening, which at once sug gests the nature of the accident. On the shoul der there is a large triangular muscle, the deltoid, which lifts the arm from the side. At the back is the triceps, which extends the fore arm; in front are two muscles which flex or bend it—the biceps and the braehialis antieus; and on each side below are muscles passing to the forearm and hand: while above the great muscle of the hack (latissimus dorsi) and that of the chest (the peetoralis major) are inserted on each side of a groove, wherein lies one of the tendons of the biceps (q.v.), The motions of
the ulna are flexion or bending effected by the biceps, and extension or straightening by the braehialis antieus and the triceps, its projec tions being received in these movements into corresponding depressions on the humerus. The movements of the hand are principally due to the radius, the head of which rolls upon the ulna, thereby turning the palm downward (prona tion), or restoring the palm upward supina tion) , these movements being effected by muscles, two for each movement, which, taking their fixed points from the humerus and ulna, pull the radius round on the latter. The elbow-joint is ginglymoid or hinge-like, and therefore has strong lateral ligaments; but it is often liable to dislocations, which may be accompanied by fracture. The accident being often followed by severe inflammation, the joint is very apt to stif fen (see ANKYLOSIS) , thereby seriously impair ing the ucafulness of the limb; it is, therefore, unadvisable to keep the limb too long in any one position after such an injury. (See JOINTS, DIS EASES OF.) The upper extremity is supplied with blood by the brachial artery, the continua tion of the axillary trunk. The veins collect into large superficial trunks, which unite at the bend of the elbow, at which situation one may be selected for venesection, and then pass on to the axillary, on the outside by the cephalic vein, on the inner side by the basilic. Deep veins also accompany the arteries and pass upward to join the axillary at its commencement.
The nerves pass down as large cords by the side of the artery, and diverge from it to their ultimate distributions; the musculo-spiral soon passing round at the back to appear on the outside, to become the radial and posterior interosseous nerves; the ulnar running behind the internal condole, for which it has obtained the term 'funny bone,' from the electric - like thrill winch passes along the arm when the nerve is struck or pressed. The median, as its name implies, keeps a middle course with the artery.
In wounds of the forearm, bleeding is some times excessive. It may be at once controlled by pressure on the brachial artery, on the inner side of the biceps.
The arm affords excellent illustrations of some of the principles of mechanics. The insertion of the muscles so near, as will be seen, to the fulcra or centres of motion, involves a loss of power in the usual sense of the word; there is, however, a corresponding gain in velocity at the end of the lever, and for most of the purposes to which the hand is put, agility is of far greater moment than mere strength.