THE INTERNAL EAR OR LABYRINTH 



773 



through a small orifice in the tip of the cochlea, which is known as 

 the helicotrema. 



FIG. 389. MEMBRANOUS LABYRINTH OF THE RIGHT SIDE, SEEN FROM THE EXTERNAL 



SURFACE. 



1, Utricle; 2, superior semicircular canal; 3, posterior semicircular canal; 4, external 

 semicircular canal; 5, saccule; 6, endolymphatic canal, with 7 and 7', its two branches, 

 and 8, its vestibular cul-de-sac; 9, cochlear canal, with 9', its vestibular and 9", its 

 terminal cul-de-sac; 10, canalis reunions of Hensen. (American Text-book of Physio- 

 logy.') 



These two scalae, therefore, are separate tubes. The scala vestibuli 

 ascends from the vestibule into the tip of the cochlea, while the scala 



B 



FIG. 390. FIG. 391. 



FIG. 390. CROSS-SECTION THROUGH THE COCHLEA, SHOWING THE DIFFERENT WINDINGS 



OF THE CANALS. 



M, modiolus, with the branches of the cochlear division of the auditory nerve; 

 S, spiral ganglion; b, basilar membrane with the organ of Corti; s-v, scala vestibuli; 

 s-t, scala tympani; c, central canal. 



FIG. 391. DIAGRAM ILLUSTRATING THE VIBRATION IN OPPOSITE DIRECTIONS OF THE 



MEMBRANES CLOSING THE FENESTRA OVALIS AND ROTUNDA. 

 S, stapes; o, fenestra ovalis; r, fenestra rotunda. 



tympani descends from here to the fenestra rotunda. Both are 

 filled with perilymph, and the vibrations set up by the oscillations 



