other matter from the ear to the pharynx. Occasionally in a cold or for some other reason they become stopped up and trouble results in the middle ear. Some of the mastoid cells also connect with the middle ear and may become infected, causing mastoid disease.
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Fig. 22.—Interior view of left bony labyrinth after removal of the superior and external walls: 1, 2, 3, the superior, posterior, and external or horizontal semicircular canals; 4, fovea hemi-elliptica; 5, fovea hemispherica; 6, common opening of the superior and posterior semicircular canals; 7, opening of the aqueduct of the vestibule; 8, opening of the aqueduct of the cochlea; 9, the scala vestibuli; 10, scala tympani; the lamina spiralis separating 9 and 10. (From Quain, after Sömmerring.)
The internal ear consists of various chambers hollowed out in the petrous portion of the temporal bone. There is an osseous labyrinth, consisting of a central cavity known as the vestibule, three semicircular canals, and the cochlea, and within the osseous labyrinth, surrounded by perilymph, is the membranous labyrinth, of like form, filled with the endolymph. Communication exists externally with the middle ear by the round and oval windows and internally with the internal auditory canal, through which passes the eighth cranial or auditory nerve, the special nerve of hearing, which is distributed to the inner ear only. When the auditory nerve enters the ear through this internal auditory meatus it divides into two branches, of which one goes to the vestibule and the other to the
