€ii 



THE EAE, 



The first coil, being much the widest in its curve and composed of the 

 largest portion of the tube, nearly hides the second turn from view ; 



Fitr. 456. 



FiK. 457. 



Fig. 450. — DiAGKAM.MATIC YlEW OF THE OsSEOUS CoCHLEA LAID OPEN. 



1, modiolus or central j)illar ; 2, placed on three turns of the lamina sinralis ; 3, scala 

 tympani ; 4, scala vestibuli. 



Fig. 457. — View op the Osseous Cochlea divided through the Middle 

 (from Arnold). | 



1 , central canal of the modiolus ; 2, lamina spiralis ossea ; 3, scala tympani ; 4, scala 

 vestibuli ; 5, porous substance of the modiolus near one of the sections of the canalis 

 spiralis modioli. 



and, bulging somewhat into the tympanum, forms the round elevation 

 on the inner wall of that cavity called the promontory. 



The modiolus (columella cochlese) forms the central pillar or axis 

 around which the tube and lamina turn spirally. It is much the 

 thickest within the first turn of the cochlea, rapidly diminishing in 

 size in the succeeding parts. The outer surface is dense, being, in 

 fact, composed of the walls of the spiral tube ; but the centre is 

 spongy as far as the last half coil, and is pierced by many small 

 canals, for the passage of the nerves and vessels to the lamina spiralis : 

 one of these canals, larger than the rest {canalis centralis modioli), runs 

 from the base through the centre of the modiolus. 



The lamina s])iraiis ossea is a thin, flat plate, growing from and wind- 

 ing around the modiolus, and projecting into the spiral tube, so as to 

 divide it partly into two. Its free margin, wliich gives attachment in 

 the recent state to the membranous septum, does not reach farther than 

 about half of the distance between the modiolus and the outer wall of the 

 spiral tube. The osseous lamina terminates close to the apex of the cochlea 

 in a hooklike process {liamulus), which partly bounds the helicotrema. 



The lamina is thin and dense at its free margin ; but nearer the 

 modiolus it is composed of two dense outer plates enclosing a more 

 open and spongy structure, in which are numerous small canals for 

 vessels and nerves, continuous with, but running at right angles to, the 

 canals in the modiolus. Winding around the modiolus, close to the 

 lamina spiralis, is a small canal, named by Rosenthal the canalis 

 spiralis modioli. 



The scalcc in the osseous cochlea are two in number, distinguished as 

 the scala tympani and scala vestibuli. 



The scala tympani, the portion of the tube on the basal side of the 

 lamina spiralis, commences at the fenestra rotunda, Avhere in the recent 

 state it is separated from the tympanum by the secondary membrane of 

 the tympanum. Near its commencement is the orifice of a small canal 

 (aquediirtus cochlecc, fig. 453, 9), which extends downwards and inwards 

 tluxHigh the substance of the petrous part of the temporal bone to near 



