516 STUDIES IN ADVANCED PHYSIOLOGY. 



where the partition is missing the sound wave reaches the 

 scala tympani and, (4) then descends the scala tympani to 

 the round foramen by the movements of the membrane of 

 which it is (5) finally led back into the middle ear and 

 so lost. A sound wave does not, therefore, go into the 

 internal ear to be there lost, but is passed through the same 

 in such a way, that the reflection of a sound wave back- 

 wards in the form of an echo is prevented. It is evident 

 that if one vibration after another should run into the peri- 

 lymph, that unless these vibrations could pass out again 

 they would be reflected back, and meeting new vibrations 

 entering produce a confusion that would preclude the pos- 

 sibility of distinctly hearing. We shall see that the ear 

 perceives these waves as they pass unhindered by. 



Having examined the bony labyrinth it is possible to 

 place in it more intelligently the real sensory or membran- 

 ous part. 



THE MEMBRANOUS EAR. 



In the vestibule the membranous ear consists of two 

 sac-like expansions connected by means of a narrow bridge. 

 The sac nearest the cochlea is called the sacculus, the one 

 nearest the semicircular canals the utriculus. The sacculus 

 and utriculus float in the perilymph. They are hollow struc- 

 tures and are filled with a liquid called the endolymph. As 

 the membranous ear is an entirely closed structure the peri- 

 lymph around it and the endolymph within it are in no place 

 in direct communication. 



Arising from the utriculus are three membranous semi- 

 circular canals which pass through the bony semicircular 

 canals, occupying, however, only a relatively small part of 

 the space of these. On one limb of each semicircular canal 

 near to where it arises from the utriculus there is a marked 

 expansion called an ampulla. This dilatation is shared by 

 the bony canal as well. 



Connected with the sacculus there is a small tube which 

 leads into the cochlea and extends to the very top. This is 

 the membranous cochlea. It is really nothing but a tube- 



