INTERNAL EAR 



607 



the hair cells in such a way that, when they come in contact with the niem- 

 brana tectoria, further movement of the basilar membrane is prevented. 



S-C 



FIG. 306. The membranous labyrinth. 

 CM, canalis or scala media of the 

 cochlea ; s, saccule ; u, utricle ; sr, semi 

 circular canals. 



FIG. 307. Vertical section through the 

 cochlea. 



The way in which motion is imparted to this membrane by the ossicles 

 may be described as follows. The osseous labyrinth communicates with the 

 middle ear by means of two openings, the oval window and the circular win- 

 dow. The oval window connects with the upper of the three cochlear canals, 

 via the vestibular. The upper canal is therefore called the scala vestibuli. 

 The lower canal connects with the round window only, and since the round 

 window is fitted with a membrane, the canal gets the name scala tympani 

 (drum or membrane). Fitting into the oval window is the plunger of the 

 stapes, and between the two is the annular seal which permits motion of the 

 plunger without allowing escape of the perilymph from the labyrinth. 



FIG. 308. Vertical section of the first turn of the human cochlea. (G. RETZIUS.) 

 s.v. scala vestibuli ; s.t, scala tympani ; d.c, scala media ; sp.l, spiral lamina ; n, nerve 

 fibres ; l.sp, spiral ligament ; str.v, stria vascularis ; s.sp, spiral sulcus ; R, section of 

 Reissner's membrane; I, limbus laminae spiralis ; m.t, membrana, tectoria ; tC, tunnel 

 of Corti ; b,m, basilar membrane ; h.i, h.e, internal and external hair-cells. 



