290 HUMAN PHYSIOLOGY 



2. The lamina spiralis membranacea forms the continua- 

 tion of the lamina ossea and extends to the outer wall of the 

 cochlea. It is formed by the basal membrane (), composed 

 of parallel transverse fibres, and contains the apparatus for 



FIG. 41. CROSS-SECTION OF ONE OF THE COILS OF THE COCHLEA. 

 (After Rauber.) 



SV, scala vestibuli; S T, scala tympani; CC, canalis cochlea; Iso, lamina 

 spiralis ossea; b, membrana basilans; from Us to Isp, lamina spiralis mem- 

 branacea; Co, organ of Corti; nc, nerve bundle; K, membrane of Reissner. 



auditory sensations, i.e. organs of Corti (Co), placed upon 

 the basal membrane. Each organ of Corti consists of: 



1. The pillars of Corti (CC, Fig. 42), i.e. two pillars bent 

 in the form of the letter 5, resting on the membrana basi- 

 laris. One is called the inner, the other the outer, pillar, 

 and the two unite at the top. 



2. The cells of Corti or hair cells (/*), cylindrical cells 

 of which one is placed internal and three or four external to 

 the pillars. At their free surface they are provided with 

 small hairs which project through perforations of a support- 

 ing membrane, the membrana reticularis. Above this is 

 placed another membrane, the membrana tectoria (Mt). 



The membrane of Reissner (R, Fig. 41), which proceeds 

 obliquely upward from the lamina spiralis ossea and unites 

 with the upper wall of the cochlear canal, separates the 

 canalis cochleae (C C, Fig. 41), in which the organs of Corti 

 are placed, from the scala vestibuli. The canalis cochleae 



