^^ A MANUAL OF ANATOMY 



wall of the saccule, and is also lined with auditory epithelium, 

 covered by otoliths. The crista acustica, as stated, is the free 

 margin of the septum transversum in each ampulla, and is covered 

 by auditory epithelium. 



The auditory epithelium is of the columnar variety, and consists 

 of two kinds of cells, auditory and sustentacular. The auditory 

 €ells are nucleated, and each is provided at its free extremity with a 

 slender, tapering, hair-like filament, which projects into the cavity. 

 These filaments are sometimes spoken of collectively as auditory 

 hairs, and the cells are hence called hair-cells. Their deep ex- 

 tremities fall short of the membrana propria. The sustentacular 

 €ells lie between the hair-cells, and are elongated and nucleated. 

 Their deep extremities are attached to the membrana propria, and 

 their free extremities give rise to a kind of limiting membrane. 

 The auditory nerve-fibres pierce the membrana propria, and, having 



Superior Semicircular Canal 



External Semicircular Canal JjC^ \. Crus Commune of Superior and 

 _>tT— <N, ^> Posterior bemicircular Canals 



Posterior Semicircular Canal /? VnV'') /\ Ampulla 



•A ^j j^-^/ fl^-f Nerve to Ampulla 

 "^^^-^^f^Jli^r. Nerve to Utricle 

 c^^^^Mjjt ^BI Nerve to Saccule 



^VB\iW/^ Cochlear Nerve 



Facial Nerve '' ^Mlff 



Fig. 651.— The Membranous Semicircular Canals, showing the Dis- 

 tribution OF THE Branches of the Auditory Nerve to their 

 Ampullae (Breschet). 



lost their medullary sheaths, the axons terminate in arborizations 

 around the deep ends of the auditory or hair cells. 



Membranous Cochlea. — The membranous cochlea is situated 

 within the osseous cochlea, and completes the deficiency which is 

 left by the lamina spiralis. It consists of two membranes, namely, 

 the basilar membrane and the membrane of Reissner, which 

 enclose between them the ductus cochlearis, or scala media. The 

 osseous cochlea in the recent state is therefore divided into three 

 spiral passages, namely, (i) the scala t3niipani, (2) the scala vesti- 

 buli, and (3) the scala media. The scala vestibuli is continuous 

 with the scala t5nTipani at the cupola through means of an aperture, 

 called the helicotrema ; and at the base of the cochlea it opens upon 

 the anterior wall of the vestibule. The scala tympani commences 

 at the fenestra rotunda, and in the recent state is separated from 

 the tympanic cavity by the secondary membrane of the tympanum. 

 The scala media, or ductus cochlearis, communicates, near its lower 

 end, with the saccule by means of the canalis or ductus reuniens 

 of Hensen. The scala vestibuli and scala tympani contain peri- 



