FUNCTIONS OF THE HYPO-GLOSSAL NERVE.

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absence of any ganglionic enlargement upon the trunk of the nerve) would seem to indicate that the function of the hypoglossal is essentially motor; and such a conclusion is sustained by the experiments of Longet, who found the nerve incapable of transmitting any sensory impressions when the roots were subjected to irritation.

Mayo and Magendie, however, first proved that the nerve possessed sensory filaments, after it had escaped from the cavity of the cranium, which results have since been confirmed by most of the later physiologists. We can easily explain this acquired power of sensibility which the nerve exhibits, by the branches of communication which it receives from the pneumogastric, the cervical nerves, and the gustatory branch of the fifth nerve; so that there is little, if any, reason to doubt that the original fibers of the nerve itself are purely motor in function.

In connection with the glosso-pharyngeal nerve, I entered into a somewhat extended discussion of the mechanism of the act of deglutition;' and the same subject might, with equal propriety, be again repeated in connection with the hypoglossal nerve, since both are intimately associated with those complex movements. It will suffice, however, to again call attention to the fact, that movements of the tongue were of the greatest importance in swallowing, since that organ not only conveyed the bolus to the back portion of the mouth, and, when liquids were to be swallowed, helped to form a tube through which a suction force could be exerted, but also assisted in the prevention of food from entering the cavity of the larynx.

CLINICAL POINTS PERTAINING TO THE HYPO-GLOSSAL NERVE.

When this nerve is divided in animals, the sense of taste remains and the tongue retains its normal sensitiveness; but the power of movement is utterly destroyed if the nerves of both sides are simultaneously cut. As a natural consequence, the first stage of the act of deglutition is materially embar

See page 472 of this volume.

rassed, and the second stage is liable to be associated with the entrance of fluid, if swallowed, into the cavity of the larynx.

When, in the human subject, this nerve is impaired, either as a special type of paralysis or during an attack of hemiplegia, the power of protrusion of the tongue from the mouth in a straight line is lost, and that member becomes deflected toward the side which is paralyzed, since the geniohyo-glossus muscle is unopposed. A disease of rather rare occurrence, in which the hypo-glossal nerves of both sides are paralyzed, and, in addition, the orbicular muscle of the mouth, and, not infrequently, the intrinsic muscles of the larynx, is described by Duchenne; and, since his article, it has been

FIG. 152.-Glosso-labio-laryngeal paralysis. (After Hammond.)

written upon by most of the later authors under the names of glosso-labio-laryngeal paralysis, glossoplegia, etc. In this type of disease the tongue lies motionless and trembling in the

DUCHENNE'S DISEASE.

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floor of the mouth, if all power of motion be paralyzed; but, if paresis only exist, it can be imperfectly protruded with difficulty, and is tremblingly and slowly retracted. If one side be affected, the sound side becomes full and prominent, in comparison with the affected side, when called into action. The peculiar trembling character of the movement of the tongue in bilateral paresis is observed in every motion which the patient attempts to perform with that organ, and all the motions are slowly and imperfectly accomplished.

The most important effects of the paralytic state of the muscles are shown in attempts at mastication and speech. The food is no longer properly placed between the teeth; is with great difficulty carried to the back part of the mouth; and frequently regurgitates into the mouth, when attempts are made to swallow. The saliva is secreted in large quantities, and is swallowed with extreme difficulty, so that the patient is constantly obliged to expectorate.

FIG. 153. Glosso-labio-laryngeal paralysis. (After Hammond.)

The disturbances of speech may present themselves with varying degrees of intensity. In those cases where the tongue is affected upon one side only (and a state of paresis exists, rather than that of complete paralysis of motion), only those sounds which require the aid of the tongue to be pronounced

are indistinctly and incompletely articulated. These letters are s, sh, l, e, i, and, at a later period, k, g, r, etc.

When the paralysis is bilateral, and the tongue has undergone atrophy, the speech becomes exceedingly indistinct, muttering and inarticulate, so that the patient can hardly express himself in sounds that can be understood by those in constant communication with him. The act of singing is always affected in even the mild forms of lingual paralysis; and the falsetto notes are particularly affected, since the tongue plays an important part in so directing the sound as to give it its proper timbre.

The effects of lingual paralysis must not be confounded with spasm of the lingual muscles (the act of stuttering), or, on the other hand, with dumbness and aphonia.

In some cases of Duchenne's disease, the lips are not affected; while, in others, the laryngeal and pharyngeal muscles are not impaired to a sufficient degree to cause any serious impediment to their normal functions. We can the better understand why all possible varieties and degrees of paralysis may exist in this disease when we consider that, in order to account for all the symptoms present in a fully developed case, the facial, spinal accessory, pneumogastric, and hypo-glossal nerves must be simultaneously diseased, or subjected to extreme pressure. Should the facial nerve escape, the lips and face will preserve their normal power; if the spinal accessory nerve be unimpaired, the larynx may escape, provided that the pneumogastric nerve remain intact below the point of communication between these two nerves; if the hypo-glossal nerve be normal, the symptoms referable to the tongue would not be detected. The essential lesion of this disease seems to consist of a degeneration of the medulla oblongata and the upper portion of the spinal cord; hence the nuclei of origin of the facial, spinal accessory, pneumogastric, and hypo-glossal nerves are liable to be involved to a greater or less extent simultaneously. Whether the view of Leyden, that the condition is one of myelitis, will be sustained, is still uncertain, but that the condition closely re

GLOSSO-LABIO-LARYNGEAL PARALYSIS.

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sembles that which creates the spinal paralysis of the infant and adult seems positive.

The previous existence of the early manifestations of syphilis and the probable activity of the disease in the system may account for the lesion in some cases, while in others the rheumatic diathesis, mental anxiety, and excessive mental application,' seem to have acted as exciting causes.

The general paralysis of the insane often first manifests itself in a peculiar weakness of the tongue and lips.

The tremor of paralytic dementia probably first makes its appearance in the facial and lingual muscles. It consists in non-rhythmical contractions of small muscles or of fasciculi of muscles, which are either present in the quiescent state of the features, or are excited by emotion or by the performance of a voluntary movement, as showing the tongue or teeth. Sometimes innumerable fine, fibrillary tremors cover the face, while, in some cases, the movements are coarser, and irregular enough to merit the term choreic. The tongue exhibits both sets of tremors--the very fine fibrillary ones and the large choreic oscillations. There is, also, though usually at a later stage, some shriveling or atrophy of the tongue. I quote from a late article of Professor E. C. Seguin,' as follows:

"The hands are tremulous, usually in a fine, semi-rhythmical way. This trembling is sometimes scarcely visible, but is perceptible as a delicate parchment-like fremitus on holding up the patient's extended fingers between ours. In the lower extremities the tremulousness is not apparent.

"The speech is affected as a result of this tremor, and as the result of a certain want of coördination in the muscles of articulation. Words are quickly spoken, with some syllables omitted or blurred, or with a terminal syllable left off. The articulate sounds which are produced are heard as vibratory or tremulous, and the speech seems thick. Patients semi-unconsciously avoid long or difficult words in conversation, and

Such cases as these are reported in the admirable description of this complicated affection by my colleague and friend Professor W. A. Hammond: "Treatise on the Diseases of the Nervous System." New York: D. Appleton & Co., 1876.

༔ "Med. Record," 1881.