866 THE ORGANS OF SPECIAL SENSE. 



project and are arranged in the form of a crescent, the concavity of which opens 

 inward. The deep ends of the cells are rounded and contain large nuclei : they 

 reach only as far as the middle of Cord's rods, arid are in contact with the 

 ramifications of the nervous filaments. Between the rows of the outer hair-cells 

 are rows of supporting cells, called the cells of Deiters ; their expanded bases are 

 planted on the basilar membrane, while their opposite ends present a clubbed 

 extremity or phalangeal process. Immediately to the outer side of Deiters's cells 

 are some 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 Kolliker is a delicate framework 

 perforated 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 rows 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's cells. 



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

 toria, or membrane of' Corti, which is attached to the vestibular surface 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's cells (Retzius). 



The inner surface of the osseous labyrinth is lined by an exceedingly thin 

 fibre-serous 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, arid through the helico- 

 trema into the scala tympani. A delicate tubular process is prolonged along the 

 aqueduct of the vestibule to the inner surface of the dura mater. This membrane 

 is continued across the fenestra ovalis and rotunda, and consequently has no com- 

 munication 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 aqua 

 labyrinthi, liquor Cotunnii, or perilymph (Blainville). 



The scala media 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 heli- 

 cotrema ; the lower end is lodged in the recessus cochlearis of the vestibule. Near 

 this blind extremity, the scala media receives the canalis reuniens of Hensen (Fig. 

 462), a very delicate canal, by which the ductus cochlearis is brought into con- 

 tinuity with the saccule. 



The arteries of the labyrinth are the internal auditory, from the basilar, and 

 the stylo-mastoid, from the posterior auricular. The internal auditory divides at 

 the bottom of the internal meatus into two branches : cochlear and vestibular. 



The cochlear branch subdivides into from twelve to fourteen twigs, which 

 traverse the canals in the modiolus, and are distributed, in the form of a capillary 

 network, in the substance of the lamina spiralis. 



The vestibular branches accompany the nerves, and are distributed, in the 

 form of a minute capillary network, in the substance of the membranous labyrinth. 



The veins (auditory) of the vestibule and semicircular canals accompany the 

 arteries, and, receiving those of the cochlea at the base of the modiolus, terminate 

 in the posterior part of the superior petrosal sinus or in the lateral sinus. 



The auditory nerve, the special nerve of the sense of hearing, divides, at the 



