INTERNAL EAR. 529 



which is continuous, through the Eustachian tube, with that of 

 the guttural pouch and pharynx, and is reflected into the mastoid 

 cells. The whole of this membrane is lined with epithelium, 

 that in the tube being ciliated. 



INTERNAL EAR. 



The internal ear, from its complexity termed the labyrinth, is 

 the ultimate part of the organ of hearing. It consists of a cavity 

 whose boundaries include 

 an osseous outer, and a 

 membranous inner por- 

 tion, respectively termed 

 the bony and the mem- 

 branous labyrinths. 

 The bony labyrinth is an 

 irregular cavity, divided 

 into three separate parts ; 

 the vestibule, semicircu- 

 lar canals, and cochlea. 



The Vestibule is an 

 irregular, oval - shaped 

 cavity, situated between 

 the cochlea and the semi- 

 circular canals, having 

 the fenestra ovalis pene- 

 ti'ating its outer wall, 

 and the five round open- 

 ings of the semicircular 

 canals at its back. At 

 the upper part of its 

 inner wall are two de- 

 pressions, the fovea 



Tig. 203. 



Diagram of the ear. In the internal portion, the black 

 part shows the cavities of the bony, and the white part those 

 of the membranous labyrinth. Cm, Cavity of the concha; 

 aG, External auditory meatus: Tr, Tympanic membrane; 

 elliptica^ and fovea C*. Tympanum; Ak, Auditory ossicles; Fr, Fencs ra 

 , . J , , rotunda ER, Eustachian tube ; L, Guttural pouch ; Sac, 



hemiSpheriCa, separated Sacculus : ut, Utricle ; oB, uB, Bouy-Co, HB, Membranous 

 bv n ridcrp thp Pmi- semicircular canals; Be, Aquaeductus ve«tibuli ; Sc, Saccus 

 J o ' endolymphaticus . St, Scala tympani • Sv, Scala vestibuli ; 



nentia 'pyraDlidalis, all Con, Scala intermedia; +, Its vestibular caecal sac; Cr, 

 o ^ • ^ • 1-1 Ductus reuniens ; *, Its apex ; Dp, Aquaeductus cochleae, vel 



of which are pierced by cotunnii. 

 numerous small open- 

 ings, macula cribrosa, for the passage of nerve filaments. Behind 

 the fovea hemispherica is the opening of the aqueduct of the 



2 M 



