ANATOMY OF THE INTERNAL EAR. 213 



the membrana tympani the degreee of tension most favorable 

 for vibration under the influence of certain tones, puts the 

 chain of bones in the condition best adapted to the conduc- 

 tion of the vibrations of the membrane to the labyrinth, with 

 the smallest possible loss of intensity. 



Physiological Anatomy of the Internal Ear 



The internal ear consists of the labyrinth, which is di- 

 vided into the vestibule, semicircular canals, and cochlea. 

 The general arrangement of these parts has already been de- 

 scribed ; 1 and it only remains for us to study the structures 

 contained within the bony labyrinth, in so far as their anat- 

 omy bears upon the physiology of audition. The most deli- 

 cate and complicated points, by far, in the anatomy of the 

 auditory apparatus are connected with the histology of the 

 internal ear, which, since the researches of Corti, has been 

 studied very closely, particularly in Germany. We shall 

 avoid, however, the discussion of histological questions of 

 purely anatomical interest, and confine ourselves to those 

 points which have a direct bearing upon physiology. 



Passing inward from the tympanum, the first division of 

 the internal ear is the vestibule. This cavity communicates 

 with the tympanum by the f enestra ovalis, which is closed 

 in the natural state by the base of the stapes. It communi- 

 cates, also, with the semicircular canals and with the cochlea. 



General Arrangement of the Membranous Labyrinth. 

 The bony labyrinth is lined by a moderately-thick periosteum, 

 consisting of connective tissue, a few delicate elastic fibres, 

 numerous nuclei, and blood-vessels, with spots of calcareous 

 concretions. This membrane adheres closely to the bone and 

 extends over the f enestra ovalis and the f enestra rotunda. Its 

 inner surface is smooth and covered with a single layer of cells 

 of pavement-epithelium, in some parts being segmented and 

 in others forming a continuous nucleated sheet. In certain 



1 See page 163. 



