THE INTERNAL EAR, OR LABYRINTH 1149 



five or six rows of columnar cells, the supporting cells of Hensen. Their bases are 

 narrow, while their upper parts are expanded and form a rounded elevation on 

 the floor of the ductus cochlearis. The columnar cells lying outside Hensen's 

 cells are termed the cells of Claudius. A space is seen between the outer rods 

 of Corti and the adjacent hair cells; this is called the space of Nuel. 



The lamina reticularis, or membrane of Kb'lliker, is a delicate framework perfo- 

 rated by rounded holes. It extends from the inner rods of Corti to the external 

 row of the outer hair cells, and is formed by several row r s of "minute fiddle-shaped 

 cuticular structures" called phalanges, between which are circular apertures . 

 containing the free ends of the hair cells. The innermost row of phalanges 

 consists of the phalangeal processes of the outer rods of Corti; the outer rows are 

 formed by the modified free ends of Deiters' cells. 



Covering over these structures, but not touching them, is the membrana tectoria 

 or membrane of Corti (Figs. 852 and 856), which is attached to the vestibular sur- 

 face of the lamina spiralis close to the attachment of the membrane of Reissner. 

 It is thin near its inner margin, and overlies the auditory teeth of Huschke. Its 

 outer half is thick, and along its lower edge, opposite the inner hair cells, is a 

 clear band, named Hensen's stripe. Externally, the membrane becomes much 

 thinner, and is attached to the outer row of Deiters' cells (Retzius). It is made 

 up of multitudes of delicate fibres embedded in a transparent matrix of a soft, 

 transparent collagenous character with marked adhesiveness (Hardesty). 



The osseous labyrinth is lined by an exceedingly thin fibroserous membrane, 

 analogous to a periosteum, from its close adhesion to the inner surfaces of these 

 cavities, and performing the office of a serous membrane by its free surface. It 

 lines the vestibule, and from this cavity is continued into the semicircular canals 

 and the scala vestibuli of the cochlea, and through the helicotrema into the scala 

 tympani. A delicate tubular process is prolonged along the aqueduct of the vesti- 

 bule to the inner surface of the dura. This membrane is continued across the 

 fenestra ovalis and fenestra rotunda, and consequently has no communication 

 with the lining membrane of the tympanum. Its attached surface is rough and 

 fibrous, and closely adherent to the bone; its free surface is smooth and pale, 

 covered with a layer of epithelium, and secretes a thin, limpid fluid, the perilymph. 



The scala media (ductus cochlearis) is closed above and below. The upper blind 

 extremity is termed the lagena, and is attached to the cupola at the upper part of 

 the helicotrema; the lower end is lodged in the recessus cochlearis of the vesti- 

 bule. Near this blind extremity, the scala media receives the canalis reunions of 

 Hensen (Fig. 850), a very delicate canal, by which the ductus cochlearis is brought 

 into continuity with the saccule. 



The auditory nerve (n. acusticus), the special nerve of the senses of hearing 

 and of equilibrium, divides, at the bottom of the internal auditory meatus, into-* 

 two branches, the cochlear and vestibular. /<**/ 



^^^- 



The vestibular nerve (n, vestibularis), the posterior of the two, presents, as it " 

 lies in the internal auditory meatus, a ganglion, the vestibular ganglion or the 

 ganglion of Scarpa (ganglion ivstibulare); the nerve divides into three branches 

 which pass through minute openings at the upper and back part of the bottom of 

 the meatus (area vestibularis posterior), and, entering the vestibule, are distributed 

 to the utricle and to the ampulla of the external and superior semicircular canals. 

 The nerve filaments enter the ampullary enlargements opposite the septum trans- 

 versum, and arborize around the hair cells. In the utricle and saccule the nerve 

 fibres pierce the membrana propria of the maculae, and end in arborizations 

 around the hair cells. 



The cochlear nerve (n. cochlearis) gives off the branch to the saccule, the fila- 

 ments of which are transmitted from the internal auditory meatus through the 

 foramina of the area vestibularis inferior, which lies at the lower and back part 



