TREATMENT.--For these hysterical forms of trouble the treatment should be such as to correct, if possible, the morbid conditions upon which they {78} depend. Under the subjects of Anæsthesia, Hyperæsthesia, and Paralysis this has been sufficiently discussed. PARALYSIS AND PARESIS OF THE MUSCLES OF THE LARYNX. The function of the muscular apparatus concerned in respiration and phonation depends mainly upon the action of the recurrent nerves, as stated in the paragraph devoted to the Anatomico-physiological Facts. Disease of the centres in or near the floor of the fourth ventricle, where, in close proximity, the pneumogastric fibres of the accessory and the glosso-pharyngeal nerves take their origin, may be the sole cause of a paralysis of these muscles. Disease along the course of the nerves anywhere between this centre and the termination of the nerves may give rise to the same result. Change in the structure or function of the nerves at the point of their contact with the muscles in some instances may possibly be the sole cause of the paralysis. Alteration of the muscles themselves, such as atrophy or degeneration, produces a like effect. In certain cases both the nerves and muscles are involved in the morbid processes, but in some instances, even where there are undoubted changes in the muscles, these changes are secondary, the result of the long inactivity of the muscles. It is possible to group these morbid conditions with reference to the nerves involved; but it frequently happens that several different conditions are present at the same time, and groups of muscles supplied by different nerves are simultaneously involved. It is therefore difficult to classify these troubles with reference to the nerves by which the parts are supplied. The further fact that of individual muscles or parts of muscles supplied by the same nerve-trunk some are affected, while others are intact, renders this effort to make a physiological classification still more unsatisfactory. As a rule, however, we may state in general terms that diseases of the superior laryngeal nerves produce paralysis or paresis of the external tensors of the vocal cords, the crico-thyroids, and, to a certain extent, of the constrictors of the larynx. Diseases of the recurrent nerves produce paralysis or paresis of the other muscles of the organ. If the disease of the nerve is of one side only, we have, as a rule admitting of only a very few exceptions, a unilateral impairment of the motor functions of the parts. In the case of the loss of power of individual muscles or parts of muscles it is by no means easy to find a satisfactory explanation. It seems probable that in some instances the reason is to be sought in the centres, but in a great majority of cases the muscles are degenerated or the nervous filaments of the particular parts are in a morbid condition.