THE SENSE OF HEARING 



717 



fhe upper passage or scala is in free communication with the vestibule, 

 nd is known as the scala vestibuli; the lower passage or scala in the deadcon- 

 ition communicates with the tympanum by means of a round opening, the 

 iramen rotundum, and is, therefore, known as the scala tympani. In the liv- 



41 5' 6 



FIG. 322. BONY COCHLEA, i. 

 Ampulla of superior semicircular 

 canal. 2. Horizontal canal. ^3. 

 Junction of superior and posterior 

 semicircular canals. 4. The pos- 

 terior semicircular canal. 5. Fora- 

 men rotundum. 6. Foramen ovale. 

 7. Cochlea. 



FIG. 323. i. Utricle. 2. 

 Saccule. 3. Vestibular end of 

 cochlea. 4. Canalis reuniens. 

 5. Membranous cochlea. 6. 

 Membranous semicircular 



canals. 



;ing condition this opening is completely closed by a membrane, a second 

 membrana tympani. Both the scalae vestibuli and tympani communicate 

 at the apex of the cochlea by a small opening, the helicotrema. The 

 modiolus, the central bony axis, is perforated from base to apex by 

 a canal for the passage of the auditory nerve-fibers; lateral canals, diverg- 

 ing from the central canal, pass through 

 the osseous lamina spiralis and transmit 

 fibers of the auditory nerve. The interior 

 f the bony labyrinth is lined by periosteum 

 1 jvered by epithelium and in communication 

 with lymph-spaces at the base of the ^ skull 

 by means of the aqueduct of the vestibule. 



The membranous labyrinth, lying 

 within the osseous labyrinth, corresponds 

 with it in form, though it is smaller in size. 

 It may be subdivided into vestibule, semi- 

 circular canals, and cochlea (Fig. 323). 



The Vestibular Portion. The vestibular 

 portion consists of two small sacs, the utricle 

 and the saccule, which communicate with 

 each other by means of the two branches of 

 a duct passing through the aqueduct of the 

 vestibule the ductus endolymphaticus. 



The Semicircular Canals. The semicir- 

 cular canals, three in number, communicate 

 with the utricle in the same manner as the bony canals communicate with 

 the vestibule The saccule communicates with the membranous cochlea 

 by a short canal, the canalis reuniens. The walls of the utricle, saccule ar 

 semicircular canals are composed of connective tissue lined by epithelium 

 At the points of entrance of the auditory nerve, the macula acusttca, in all 



FIG. 324. SECTION OF WALL OF 

 UTRICLE or THE INTERNAL EAR, 

 through macular region, from 

 rabbit, showing otoliths (o), em- 

 bedded within granular substance 

 (g). h. Ciliated cells with proc- 

 esses. (/>), extending between 

 sustentacular elements (s). m. 

 Basement membrane, n. Nerve- 

 fibers within fibrous tissue (D 

 passing toward hair-cells and 

 becoming non-medullated at base- 

 ment-membrane. (After Piersol.) 



