DEFINITION.--Disorders of sensation or motion, or of both sensation and motion, due to disease, first, of the centres from which the nerves of the organ are derived; second, to disease along the track of the nerves; third, to disease in the terminal distribution of the nerves; fourth, to reflected irritation from neighboring or distant parts; and fifth, to myopathic change. This last condition is not necessarily a neurosis; it is nevertheless a cause of modification of the function of the parts to which the nerves are distributed, often a result of paresis or paralysis, and therefore inseparably associated with the neuroses of the organ. Disorders of innervation, depending upon structural disease of the larynx, such as ulceration or tumor, are not included in this definition. ANATOMICO-PHYSIOLOGICAL CONSIDERATIONS.--The framework of the larynx consists of cartilages securely but rather loosely articulated with each other. The movements of these cartilages produce changes in the position and tension of the soft parts. The thyro-cricoid articulation allows ginglymoid and sliding motion; the aryteno-cricoid, rotatory and sliding motion; the hyo-thyroid, ginglymoid motion. The physiology of the muscles of the larynx is quite complex, since nearly all have fibres taking a number of different directions, and the changes in the form and positions of the parts depend upon the combined action of different muscles and parts of muscles which may be individually brought into action to produce the required results. The muscles may, however, be roughly divided into groups: 1. Constrictors of the superior strait; 2. Dilators of the superior strait; 3. Adductors of the vocal cords; 4. Tensors of the vocal cords, external, internal; 5. Relaxers of the vocal cords; 6. Abductors of the vocal cords. The superior strait of the larynx is closed by the action of the oblique portions of the arytenoideus, acting in conjunction with the ary-epiglottici, into which some of its fibres are continued, thus drawing the cartilages of Santorini downward and inward and approximating the ary-epiglottic folds and depressing the epiglottis; while the thyro-epiglottici complete the closure by further depressing the epiglottis. Fibres of the latter muscle, acting alone, may dilate the superior strait by drawing apart the ary-epiglottic folds. The transverse portion of the arytenoideus and the superior fibres of the crico-arytenoidei postici approximate the arytenoid cartilages. The crico-arytenoidei laterales, and also in a slight degree the external fibres of the thyro-arytenoidei, rotate these cartilages, turning their vocal processes inward: the action of the latter two muscles as adductors is imperfect unless the arytenoids are drawn backward and fixed by the arytenoidei postici.