732 



TEXT-BOOK OF PHYSIOLOGY 



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

 and is known as the scala vestibuli; the lower passage or scala in the dead con- 

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

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



FIG. 319. 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. 320. 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 

 Ojf the bony labyrinth is lined by periosteum 

 covered 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. 320). 



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 



FIG. 324. SECTION OF WALL OF 

 UTRICLE OF THE INTERNAL EAR, 

 through macular region, from 

 rabbit, showing otoliths (o), em- 

 bedded within granular substance 

 (g). h. Ciliated cells with proc- 

 esses, (p), extending between 

 sustentacular elements (s). m. 

 Basement membrane, n. Nerve- 

 fibers within fibrous tissue (/) 

 passing toward hair-cells and 

 becoming non-medullated at base- 

 ment-membrane. (After Piersol.) 



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, and 

 semicircular canals are composed of connective tissue lined by epithelium. 

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



