INTERNAL EAK. 



531 



Fig. 204. 



Membranous labyrinth. C, Ductus cochlearis ; 



K, Its coclilear bliud end, and V, Its vestibular 



blind end ; Cr, Buctu.s reunieus ; S, Sacculus ; 



U, Utricle ; R, Aqu.neductus vestibuli. 



The Membranous labyrinth, though smaller in size, is nearly 

 the counterpart in form of the vestibule and semicircular canals, 

 and consists of two sacs within the vestibule, the larger of Avhich, 

 the utricle or sacculus covxmunis, is elongated and lodged in the 

 fovea elliptica ; the smaller, the sacculus or sacculus ijroprius, is 

 round, and lodged in the fovea hemispherica. The semicircular 

 canals, which are about one-third the size of the bony canals, 

 open by live orifices into the 

 sacculus communis. The sac- 

 culus and utricle are united 

 by an angular duct, which 

 also leads to the aqueduct of 

 the vestibule, a canal termi- 

 nating in a blind dilatation, 

 the saccus endolymphaticus. 

 The bony lamina spiralis being 

 incomplete, the division is 

 completed by two membranes, 

 the membrane of Reissnerand 

 the basilar membrane, between 

 which is the scala intermedia 



or ductus cochlearis, a tube which thus follows the turns of the 

 cochlea, originating at its apex in a blind extremity, and terminat- 

 ing in a tube, the ductus reuniens, which unites it to the sacculus. 

 This labyrinth is filled by a limpid fluid, termed the endolymj^h 

 or liquor Scarpce, and is constructed of four coats ; an external 

 serous, a vascular, a nervous, and an inner serous, from which the 

 endolymph is secreted. 



Within the sacculi are small, rounded, calcareous bodies, the 

 oto-conicc, which consist of particles of carbonate and phosphate 

 of lime, held together by animal matter ; these oto-coni« are 

 suspended from the membrane, and float freely in the endolymph. 



The Meatus auditorius internus is a bony canal, which 

 leads from the cranial cavity to the vestibule, and terminates in 

 the cribriform plate of the fovea hemispherica and eminentia 

 pyramidalis. 



The Guttural Pouches. — The mucous membrane, projecting 

 through a slit in the inferior extremity of the Eustachian tube, 

 becomes dilated into a large sac, the guttural pouch, which is 

 peculiar to the solipede and the Hyrax. These pouches, which 

 meet in the middle line, are irregular in form, are related above 



