THE INTERNAL EAE 623 



tation at their termination in the vestibule. These dilatations are 

 known as the ampullae. The osseous and membranous canals are 

 of similar shape; the latter is, of course, contained within the 

 former. 



The membranous semicircular canals open into the utricle. 

 They do not entirely fill their bony canal, but, like the utricle and 



FIG. 454. TRANSECTION OF A HUMAN SEMICIRCULAR CANAL. 



1, bone ; #, retiform connective tissue membranes ; <?, at this point a band of connect- 

 ive tissue joins the periosteum ; 4, membranous semicircular canal ; 5, ligamentous 

 attachment of the canal ; , at this point the membranous and osseous canals are in 

 contact. Moderately magnified. (After Eiidinger.) 



saccule, lie in contact with the periosteum at one surface only, this 

 surface being that of the outer wall or periphery of the semicircle, 

 while in the remaining portion of the circumference of the cylin- 

 drical bony canal, the membranous canal is loosely united to the 

 periosteum of the osseous wall by a retiform connective tissue whose 

 loose meshes are filled with perilymph. 



The wall of the membranous canal is similar in structure to 

 that of the saccule and utricle and consists of an endothelium, a 

 membrana propria, and a fibrous tunic. Each of the three ampullae 



