200 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



With the formation of canals, lagena, etc., the sensory epithelium 

 divides into separate areas (fig. 206), some of which (maculae acus- 

 ticae) have sensory cells with short hairs or bristles, while others 

 (cristas acusticae), characteristic of the ampulla?, have cells with 

 longer hairs. The membranous labyrinth is filled with a fluid, the 

 endolymph, in which are solid particles, the otoliths. These are 

 usually microscopic crystals of calcium carbonate which give the 

 endolymph a milky appearance, but in the teleosts the Hme is 



Fig. 207. Fig. 208. 



Fig. 207. — ^Labyrinth of human embryo, 30 mm. long, after Streeter. a, ampulla; 

 ac, anterior canal; c, cochlea; cr, crus; de, endolymph duct; nc, cochlear nerve; s, sac- 

 culus; se, endolymph sac; u, utriculus; v, vestibular nerve. 



Fig. 208. — Section through one of the coils of cochlea of guinea pig, after Schneider. 

 Bone lined; Is, spiral ligament; r, Reissner's or vestibular membrane; sg, spiral ganglion; 

 sm^st, sv, scalae media (ductus cochlearis), tympani and vestibuli; /, tunnel. 



aggregated into one or more 'ear stones' of considerable size. In 

 animals with open endol3miph ducts (sharks) sand from the exterior 

 may form part of the otoliths. 



With the appearance of cartilage the membranous labyrinth be- 

 comes enclosed in a protecting otic capsule (p. 67), which usually 

 follows pretty closely the divisions and canals of the epithelial parts, 

 thus forming the skeletal labjrrinth, separated from the membranous 

 labyrinth by a slight gap filled with fluid (the perilymph). When 



