64 THE ORGANS OF SPECIAL SENSE. 



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. 



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 



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 hemispherical 6, common 

 opening of the superior and posterior semicircular canals; 7, opening of the aque- 

 duct 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 Sommerring.) 



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 



