A pure, uncomplicated paralysis of the adductors of the vocal cords is extremely rare. When present it is marked by symptoms and signs which are easily recognized. A partial paralysis of an hysterical nature is, however, not unfrequently encountered. The etiology of paralysis of the lateral crico-arytenoid muscles is in most instances the same as that of the other muscles of the larynx. There may be a morbid condition of the centres in the fourth {82} ventricle, from which the spinal accessory takes its origin. It is certainly possible in theory that certain fibres ultimately distributed to these muscles may alone become diseased in their course along the trunk of the nerve. There may be change in the final distributions by which the function of the nerve is arrested. There may be myopathic change in the muscle itself, rendering it non-responsive even to normal nerve-impressions. All of these causes are theoretically possible. In fact, however, we know but little of the real causes which operate in any given case. Mackenzie, Von Ziemssen, and others ascribe it in some instances to catarrh from exposure to cold. There is developed a hyperæmia of the mucous surfaces of the supraglottic space. The structures beneath are involved in the tumefaction as a result. The voice is impaired or lost; the aphonia, which was at first due to the mechanical difficulties in the way, persists after the local inflammation has subsided. The vocal cords remain permanently apart, even though there is no swelling to prevent the arytenoids from approaching each other. Gerhardt attributes this form of paralysis in certain cases to a rheumatic inflammation affecting either the articulations or the muscles themselves. Trichina have been found in one or both muscles, producing a paresis. Syphilis, central or laryngeal, may account for a number of cases. When the loss of power is due to local syphilitic trouble, there is, however, usually a recognizable change in structure, something more than a simple paralysis. It would seem strange to find a rheumatism so localized as this hypothesis implies. Mackenzie has met with a case in which the paralysis was unilateral and toxic, due to lead-poisoning. He thinks there may be other cases of similar origin, and suggests arsenic also as a possible cause. In his case he compares this paralysis of the lateral crico-arytenoids to the loss of power in the extensors of the forearm in well-marked cases of lead-poisoning. The affection was limited to the adductor muscles. Seifert and Lublinsk in _Berlin. klin. Woch._ also report cases. The adductors only were affected. The very few cases in which this form of paralysis has been carefully noted do not supply us with the material for a more exact opinion as to the causes of the trouble.