312 DETAILED SYNTHESIS. 



864. THE MEMBRANOUS VESTIBULE is a sac nearly 

 filling the bony vestibule, floating in the peri-lymph, and 

 itself also filled with similar fluid, called endo-lymph. 



865. THE SEMICIRCULAR CANALS are three small 

 tubes at right angles to each other, opening out of the 

 vestibule (two, however, conjoining) by five orifices. 

 Each canal has an enlargement near one end. The bony 

 canals are lined with the extended lining of the vestibule 

 and filled with peri-lymph. 



866. THE MEMBRANOUS VESTIBULE is ALSO EXTENDED 

 through the canals, and correspondingly filled. Both 

 surfaces of this membrane are formed of cells. 



867. WITHIN THE MEMBRANE are small collections 

 of minute crystalline particles of carbonate of lime 

 (otolites) that adhere together and are connected with 

 the filaments of nerves that terminate in the fluid con- 

 tained in the sacs of the membranous labyrinth. 



868. THE COCHLEA is, as its name signifies, like a 

 cockle-shell in shape, and is constructed with a spiral 

 cavity like that in the cockle, turned nearly three times 

 round its axis, and rising with each turn. 



869. THE SPIRAL CAVITY is DIVIDED nearly in its 

 centre by a partition stretching across from its axis out- 

 wardly, about one third being bone, one third membrane, 

 and the other third muscular. The partition does not 

 extend quite to the top. Here both cavities unite, form- 

 ing what is called the cupola. The spiral cavities are 

 called scalse. 



870. THE MOUTH OP ONE OF THE SCALAE COMMENCES 

 at the round window; the other opens from the vestibule, 

 but does not communicate with the inside of the mem- 

 branous part. Both spirals are lined with the extended 

 lining of the bony vestibule, and filled with the same 

 peri-lymph. 



871. NERVES EXTEND UP THE AXIS OF THE COCHLEA, 



864. What is T 865. What are ? 866. How is ? 867. What are ? 

 868. What is ? 869. How is ? 870. where ? 871. How do ? 



