TRAN&ECTION OF A COIL OF THE COCHLEA. 



533 



Membrana (Mb.) tympani. The membrane is somewhat funnel-shaped as shown. 

 It is composed of three layers, the skin or cutis (see cutis), a fibrous central or intermediate 

 part and a continuation of the tympanic mucosa. The latter covers the handle of the 

 malleus and helps to bind it to the tympanum, and is only partly shown. 



M. stapedius (M. stp.). The name is connected with the bony process of the stapes to 

 which the muscle is attached ( 1438). 



M. tensor tympani (M. t. t.). There is here shown the bony process of the malleus 

 to which the tendon of this muscle is attached ( 1436). 



O. lenticulare (O. Int.). The small, nearly cylindrical bone between the stapes and 

 incus ( 1438). 



Petrosum s. perioticum. The dense bone containing the parts of the labyrinth ( 510). 



Scala vestibuli (Scl. vst.). The chamber of the cochlea opening into the vestibule. 

 It is divided into two chambers by the membrane of Reissner (Fig. 128). 



Scala tympani (Scl. tym.). This chamber of the cochlea is separated from the tym- 

 panum only by membrane. 



Stapes. The last of the small bones of the ear. Its oval base fits into the fenestra 

 ovalis. Near its small end is a bony process, to which is attached the stapedius muscle. 



Tympanum. This is the second or middle chamber of the ear ( 1434). 



Vestibulum (Vst.). The vestibule is the common chamber of the labyrinth : from it 

 extend the semicircular canals and the scala vestibuli of the cochlea ( 1431. C). 



Explanation of Fig. 128. Canalis cochleae (Cn. 

 chl.). A division partitioned off from the scala vesti- 

 buli by the membrane of Reissner. It is separated 

 from the scala tympani by the membrana basilaris 

 (Mb. bs.). 



Lamina spiralis (Lm. sprl.). This is the bony 

 partition between the two scalae. The partition is 

 completed by the membrana basilaris (Mb. bs.). It 

 arises from the modiolus and through it passes the 

 cochlear nerve (N. chl.). 



Membrana basilaris (Mb. bs.) s. lamina spiralis 

 membranacea. This with the osseous spiral lamina 

 completes the separation between the scalae. 



The organ of Corti is on the side of this membrane toward the canalis cochleae ; no 

 attempt is made to indicate it here. 



Membrana Reissneri (Mb. R.), s. lamina denticulata, s. limbus lamina spiralis. This 

 membrane divides the scala vestibuli into two parts the canalis cochlea and the scala ves- 

 tibuli proper. 



FIG. 128. TRANSECTION OF A 

 COIL OP THE COCHLEA. (From 

 Quain, after Henle.) 



