200 



GENERAL ZOOLOGY 



canal, through which the inner ear is filled with sea water, which 

 serves the same function as the endolymph of higher forms. 

 The invagination duct is attached to the sacculo-utricular canal. 

 The various parts of the inner ear constitute what is known as 

 the membranous labyrinth. It is filled with endolymph contain- 

 ing otoconia, which are microscopic crystals of calcium carbonate. 

 The "ear stones" of fishes are really large otoliths. Areas of 

 sensory epithelia consisting of large cells with long hairs, known 



ED 



A B 



Fig. 129. — A, diagram of membranous labyrinth of lower vertebrate. B, 

 membranous labyrinth of human embryo, 30 cm. in length, c, cochlea (scala 

 media); cn, cochlear nerve; ed, endolymphatic duct; l, lagena; s, sacculus; u, 

 utriculus; vn, vestibular nerve. (B after Streeter.) 



as cristae acusticae, are located in the enlarged end (ampulla) of 

 each semicircular canal, while other areas of cells with shorter 

 hairs, called maculae acusticae, are found in the utriculus, sac- 

 culus, and scala media. In mammals, including Man, the bony 

 labyrinth is the casing of bone closely following the outlines of 

 the membranous labyrinth, but separated from the latter more or 

 less completely by a perilymphatic space filled with lymphlike 

 perilymphatic fluid. In the region of the spiral cochlea the 

 perilymphatic space does not completely surround the scala 

 media. Instead it is divided into two channels, one above and 



