ETIOLOGY.--So far as we know, the causes are to be found either in central disease or hysteria. When the cause is in the centres, there is almost of necessity functional lesion of other parts of the muscular apparatus, especially of the parts supplied by the glosso-pharyngeal nerve. There will, therefore, be dysphagia. It is possible that the central lesion may be very circumscribed; in such cases we may have paralysis of individual laryngeal muscles or parts of muscles. These cases are probably very rare, and the indication of more general paralysis is, in fact, the point upon which the diagnosis of central disease depends. Tumor or other disease along the track of the spinal accessory before it unites with the pneumogastric may produce the same effect. When the affection is upon one side only the paralysis is also unilateral. There are, as before noted, exceptions to this statement. In these instances it is probable that the innervation of the affected part or side is supplied by branches from the opposite trunk. Such cases have been reported by George Johnson, Lefferts, and others. It has also been found that injury or paralysis of one recurrent nerve is sometimes followed by bilateral paralysis. Schnitzler reports a case in the _Wiener Med. Report_ for 1882. The left recurrent was compressed by aneurism of the arch of the aorta; the right was normal. There was, however, bilateral paralysis. Experiment by Tourgues[10] demonstrated the fact that powerful excitation and consequent exhaustion of one of the pneumogastrics may result in paralysis of the other. This result is in accordance with facts seen occasionally in traumatism of one of the pneumogastrics. [Footnote 10: Reported in the _Gazette de Montpellier_, Nos. 35 and 36, 1882.] A pure, uncomplicated paralysis, in which all of the muscles of the larynx are implicated, and in which no other muscles are concerned, will almost always be found to depend upon some lesion of the pneumogastrics or the spinal accessories after they leave their point of origin. Whether the paralysis is dependent upon the lesion at one point or another, the symptoms are the same so far as the larynx is concerned. The vocal cords are in a state of absolute rest between abduction and adduction; the effort at phonation gives rise to no contraction of the tensors; the arytenoids leave the cartilages slightly separated; and the state of the organ is that of muscular death.