CAUSES OF FACIAL DIPLEGIA.

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phy of both facial nerves can occur without an exciting cause of a local character being detected; and the same opinion is maintained by Pierreson,' who found a hyperplasia of the connective tissue of the nerve and the development of amyloid corpuscles to constitute the pathological changes.

This type of paralysis may be due to peripheral causes, such as exposure to intense cold, as in sleigh-riding, rheumatic inflammation of the nerves, and diseases of the petrous portion of the temporal bones (necrosis, caries, syphilitic otitis, suppurative inflammation of the middle ear, etc.).

The experiments of Schiff upon animals in whom both facial nerves had been divided, and the investigations of Trousseau, Wachsmuth,' and Davaine, have helped to clear up the effects of this double lesion, and to render its diagnosis from Duchenne's disease more positive than our previous knowledge would permit. In the human race, this condition is characterized by the following symptoms: a fixed and immovable countenance, a peculiar drooping of the angles of the mouth, a collapsed appearance of the nostrils during inspiration, a sinking inward of the cheeks during the inspiratory effort, and a protrusion or inflation of the cheek when the air is expired. The tone of the voice becomes of the most distinctly nasal quality, and the patient, from the inability to pronounce the labial consonants, is almost unable to make the simplest sentences intelligible. In consequence of paralysis of the buccinator muscles, which are supplied by the facial nerves, the act of mastication becomes embarrassed, and deglutition is greatly interfered with; hence it is not uncommon to see such patients use the finger to push the food into the grasp of the isthmus of the fauces, so as to swallow the bolus. When the head is inclined forward, the saliva runs from the mouth, in spite of all efforts to prevent it. The condition of the eyes,' which remain wide open on account of the

In both the unilateral and bilateral forms of facial paralysis, the patient often can avoid the irritation of dirt and the intense light by closing the eyelids with the pressure of the finger, or by a strip of adhesive plaster.

paralysis of the orbicularis palpebrarum muscles, affords a most important point in the discrimination between this disease and the paralysis of Duchenne. So marked is this deformity that the patient can not wink, and thus the tears are not distributed over the globe of the eye, to wash off any dust which may enter; while, on account of the paralysis of the tensor tarsi muscle, the tears are not drawn into the lachrymal sac, and therefore tend to flow over the cheek and create scalding.

THE AUDITORY, OR EIGHTH NERVE.

This nerve is strictly one of special sense, namely, that of hearing. It arises chiefly from a gray nucleus in the floor of the fourth ventricle (where its fibers form the so-called

FIG. 115.-A diagram of the auditory nerve and its branches.

1, auditory nerve, entering the meatus auditorius internus; 2, communicating filaments to the facial nerve, given off in the internal auditory canal; 3, filaments given off to supply the cochlea; 4, filaments given off to supply the posterior semicircular canal; 5, filaments given off to supply the saccule; 6, filaments given off to supply the utricle; 7, filaments given off to supply the external semicircular canal; 8, filaments given off to supply the ampullæ of the superior semicircular canal.

"lineæ transverse" which decussate in the median line), and also, in part, from three other nuclei of the medulla oblongata (page 267). Some of its fibers may be also traced to the flocculus and the nucleus fastigii and nucleus dentatus of the cerebellum. From recent statements of Lockhart Clarke, additional fibers may be traced from the auditory nucleus, which pass directly through the restiform body of the medulla. The course of the nerve, as far as the orifice of the internal

THE AUDITORY, OR EIGHTH NERVE.

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auditory canal, lies parallel with that of the facial nerve, since the same arachnoid sheath invests them both, but, before that canal is reached, a filament is given off from both these nerves to form an intermediate nerve, called the "pars intermedia," or the "nerve of Wrisberg." This intermediate portion is now supposed to be the chief source of origin of the chorda tympani nerve, and thus to be connected with the special sense of taste.

FIG. 116.-Distribution of the cochlear nerve in the spiral lamina of the cochlea (the cochlea is from the right side and is seen from its antero-inferior part). (Sappey.)

1, trunk of the cochlear nerve; 2, 2, 2, membranous zone of the spiral lamina; 3, 3, 3, terminal expansion of the cochlear nerve, exposed in its whole extent by the removal of the superior plate of the lamina spiralis; 4, orifice of communication of the scala tympani with the scala vestibuli.

The color of the auditory nerve filaments is grayish. The filaments differ from those of the other cerebro-spinal nerves (excepting those of special sense) in having a softer consistence. Some of the later researches seem to show that the filaments of this nerve are destitute of the "white substance of Schwann," and thus resemble those of the olfactory nerve, while the axis cylinders are of very large size as compared with those of other nerves. It is also claimed that small, nucleated, ganglionic enlargements can be demonstrated along the course of these fibers of the trunk of the nerve, but the minute anatomy of the auditory nerve is yet a subject for further investigation.

Within the internal auditory canal, the eighth nerve

divides into two branches, the anterior of which supplies the cochlea, while the posterior branch is distributed to the semicircular canals and to the saccule and vestibule. These two main branches are given off close to the meatus auditorius internus.

At the bottom of the internal auditory canal, the three subdivisions of the vestibular nerve pass through small open

FIG. 117.-General view of the organ of hearing. (Sappey.)

1, pinna; 2, cavity of the concha, on the walls of which are seen the orifices of a great number of sebaceous glands; 5, external auditory meatus; 4, angular projection formed by the union of the anterior portion of the concha with the posterior wall of the auditory canal; 5, openings of the ceruminous glands, the most internal of which form a curved line, which corresponds with the beginning of the osseous portion of the external meatus; 6, membrana tympani and the elastic fibrous membrane which forms its border; 7, anterior portion of the incus; 8, malleus; 9, handle of the malleus applied to the internal surface of the membrana tympani, which it draws inward toward the projection of the promontory; 10, tensor tympani muscle, the tendon of which is reflected at a right angle to become attached to the superior portion of the handle of the malleus; 11, tympanic cavity; 12, Eustachian tube, the internal or pharyngeal extremity of which has been removed by a section perpendicular to its curve; 13, superior semicircular canal; 14, posterior semicircular canal; 15, external semicircular canal; 16, cochlea; 17, internal auditory canal; 18, facial nerve; 19, large petrosal branch, given off from the ganglioform enlargement of the facial and passing below the cochlea to go to its distribution; 20, vestibular branch of the auditory nerve; 21, cochlear branch of the auditory nerve.

ings in a cul-de-sac situated at that point, and are distributed to the utricle, the saccule, and the three ampullæ.

The cochlear nerve, which is the other main branch of the auditory, enters the base of the modiolus, and its filaments

DISTRIBUTION OF AUDITORY NERVE.

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subsequently escape from the central canal of the modiolus through minute canals, which enable them to reach their point of distribution in the internal portion of the cochlea. The terminal filaments of this nerve are now believed to be connected with the spindle-shaped cells of the organ of Corti.

It is impossible, within the compass of this lecture, to enter into the minute anatomy of the ear with sufficient detail to enable you to properly appreciate the mechanism by which the waves of sounds, produced from without, are transmitted to the membrana tympani, and subsequently to the cochlea, where they are perceived by the auditory nerve filaments. To properly appreciate the difficulties which arise in determining the exact method by which the human ear is enabled to determine not only the intensity of the sound perceived, but also its pitch, quality, and musical properties, not only would the anatomy have to be given in detail, but many of the laws of physics discussed. The following general statements, however, may assist you in studying this complicated subject, and afford an explanation of some of those symptoms of disease which are referred to the ear.

The diagram shown you on the blackboard' is designed to assist you to grasp some of the principal points in the anatomical construction of the ear, which are necessary for the clear comprehension of the physiology of audition. It can be perceived that the external auditory canal and its accessory portion which we call the ear or auricle (which is placed on the exterior of the skull for the purpose of deflecting the waves of sound into that canal) lie external to the membrana tympani; and, for that reason, all of these parts, viz., the cartilages of the pinna, its ligaments, the bony canal leading to the membrana tympani, and its cutaneous lining, are included under the general term "the external ear," in contrast to the chambers which lie deeply within the temporal bone, called the middle ear, or "the carity of the tympanum," and the internal ear, or the "labyrinth."

The middle ear, or "tympanum," lies between the mem'See diagram further on in the chapter.