THE SKN-SKS. 681 



the scales of the cochlea is continuous with the perilymph in the vesti- 

 bule and semicircular canals, and there is no fluid external to its lining 

 membrane. The vestibular portion of the membranous labyrinth cam- 

 prises two, probably communicating cavities, of which the larger and 

 upper is named the utriculus; the lower, the sacculus. They are 

 lodged in depressions in the bony labyrinth, termed respectively fovca 

 hemielliptica and fovea hemispherica. Into the former open the orifices of 

 the membranous semicircular canals; into the latter the canalis cochlea. 

 The membranous labyrinth of all these parts is laminated, transparent, 

 very vascular, and covered on the inner surface with nucleated cells, of 

 which those that line the ampullae are prolonged into stiff hair-like pro- 

 cesses; the same appearance, but to a much less degree, being visible in 

 the utricule and saccule. In the cavities of the utriculus and sacculus 

 are small masses of calcareous particles, otoconia or otoliths; and the 



Fie, 402. -View of the osseous cochlea divided through the middle. 1, central canal of the 

 ibodiolus; 4 lamina spirahs ossea; 3, scala tympani; 4, scala vestibuli; 5, porous substance of 

 the mocaolus near one of the sections of the canalis spiralis modioli. X 5. (Arnold.) 







same, although in more minute quantities, are to be found in the interior 

 f some other parts of the membranous labyrinth. 



Auditory Nerve. All the organs now described are provided for the 

 appropriate exposure of the filaments of the auditory nerve to sonorous 

 ibrations. It is characterized as a nerve of special sense by its softness 

 'whence it derived its name of portio mollis of the seventh pair), and by 

 the fineness of its component fibres. It enters the bony canal (the meatus 

 tuditorius internus), with the facial nerve and the riervus intermedius, 

 nd, traversing the bone, enters the labyrinth at the angle between the 

 jase of the cochlea and the vestibule, in two divisions; one for the ves- 

 nbule and semicircular canals, and the other for the cochlea. 



There are two branches for the vestibule, one, superior, distributed 

 o the utricule and to the superior and horizontal semicircular canals, 

 and the other, inferior, ending in the saccule and posterior semicircular 

 3anal. Where the nerve comes in connection with the utricule and 

 saccule, the structure of the membrane is modified somewhat and the 

 places are called maculce acusticce. The epithelium in this region is, as 

 /re shall see directly, considerably specialized, and where the nerve is in 

 jonnection with the ampullas of the semicircular canals, too, the struct- 

 ire is altered, becoming elevated into a horse-shoe ridge, which project? 



