1346 STRUCTUEE OF CRIST A ACUSTICA. [BOOK in. 



which are maintained from some little distance down the sides, 

 and then almost suddenly cease. This is the auditory epithelium, 

 and with this alone do the nerve-fibres make connections. Seen 

 in situ (Fig. 178 A) this epithelium appears to consist of an outer 

 row of cylindrical or columnar cells (c.c.), forming the free surface, 

 and between this and the tunica propria, of a part calling to mind 

 the nuclear layers of the retina, since it appears to be composed 

 of nuclei (n.l.) closely packed together; we may speak of it as "the 

 nuclear layer." From the free surface of this auditory epithelium 

 a number of elongated, rigid, spoke-like processes (a.A.), of great 

 length in some animals such as fishes, but shorter in man, project 

 into the cavity of the ampulla; these are the auditory hairs. 

 According to some authors at all events the free surface of the 

 epithelium is guarded by a cuticular membrane, pierced for the 

 passage of the auditory hairs. 



At some little distance down the sides of the ridge, the nuclear 

 layer disappears as do also the auditory hairs ; the auditory 

 epithelium is almost suddenly transformed into a single layer 

 of epithelial cells, which differ chiefly from the epithelial cells 

 forming the general lining of the labyrinth, in that they are tall, 

 cylindrical and large, with the cell substance rich in granules. 

 These cylindrical cells, which in no way enter into connection with 

 the fibres of the auditory nerve, gradually change at some distance 

 from the auditory epithelium into the flat polyhedral cells of the 

 general lining. 



In hardened and prepared specimens the auditory hairs 

 appeared to be imbedded in a cap of mucous or fibrinous 

 material. This, which has been called the " cupula," is supposed 

 to be an artificial product, the result of a coagulation of the 

 endolymph, and not to exist during life. 



Contrary to what occurs in an epithelium elsewhere, the blood 

 vessels instead of being absolutely confined to the connective 

 tissue basis or dermis pass occasionally into the epithelium itself, 

 and form loops among the cells ; as we shall see this also occurs in 

 the cochlea. 



827. The features which we have just described may be 

 recognized without any great difficulty in sections of ampullae 

 prepared in various ways ; but considerable difference of opinion 

 obtains as to the exact nature of the constituent elements of the 

 epithelium and especially of their relations to the nerve fibres ; 

 nor is the existence of a difference of opinion to be wondered at 

 when the difficulties of investigation, greater perhaps than in any 

 other histological subject, are borne in mind. 



According to one view, the auditory epithelium consists of two 

 kinds of cells. The one kind (Fig. 178 B, 1, 2) is a cell cylindrical 

 in form or rather flask-shaped, with a flat top forming part of the 

 free surface of the epithelium, and a conical but rounded base 

 reaching less than half-way down the thickness of the epithelium. 



