Xll.] THE MEMBRANOUS LABYRINTH. 395 



semicircular canal ; b. canalis reuniens ; a. constriction l)y 

 means of which the sacculus hemisphericus S.R. is formed ; 

 /. narrowed opening between sacculus hemisphericus and 

 utriculus ; C.C. cochlea ; C.C". lumen of cochlea ; K.K. 

 cartilaginous capsule of cochlea ; K.B. basilar plate ; C/i. 

 notochord. 



connective tissue, which is more abundant around the 

 cochlear canal than around the semicircular canals. 



As soon as they have acquired a distinct connective- 

 issue coat, the semicircular canals begin to be dilated 

 it one of their terminations to form the ampullae. At 

 ibout the same time a constriction appears opposite the 

 nouth of the recessus labyrinthi, which causes its open- 

 ng to be divided into two branches one towards the 

 itriculus and the other towards the sacculus hemispheri- 

 cus ; and the relations of the parts become so altered 

 .hat communication between the sacculus and utriculus 

 ;an only take place through the mouth of the recessus 

 abyrinthi (Fig. 132). 



When the cochlear canal has come to consist of two 

 md a half coils, the thickened epithelium which lines 

 he lower surface of the canal forms a double ridge 

 rom which the organ of Corti is subsequently de- 

 eloped. Above the ridge there appears a delicate 

 ;uticular membrane, the membrane of Corti or mein- 

 rana tectoria. 



The epithelial walls of the utricle, the saccule, the 

 ecessus labyrinthi, the semicircular canals, and the 

 iochlear canal constitute together the highly complicated 

 Product of the original auditory vesicle. The whole 

 tructure forms a closed cavity, the various parts of 

 k'hich are in free communication. In the adult the 



