646 



THE EAR. 



lies within tlie sac, attached to its wall (fig. 458, ^). These otoliths are 

 crystals of carbonate of lime, rhombic, octahedral, or six-sided, often 

 pointed at their extremities. 



The ends of all the membranous semicircular canals open into the 

 utricle. 



The smaller vestibular vesicle, the saccule {II), is more nearly- 

 spherical than the common sinus, but, like it, is somewhat flattened, 

 it contains similar otoconia in its wall (fig. 458, m). The saccule is 

 situated in the lower and fore part of the cavity of the osseous vesti- 

 bule, close to the opening from the scala vestibuli of the cochlea, and 

 is received into the hollow of the fovea hemispherica, from the bottom 

 of which many branches of nerve enter it. 



A minute canal, lined with epithelium, passes from the utricle along the 

 aqueductus vestibuli to end blindly near the posterior sm-face of the petrous bone. 

 It is joined near its origin by a similar one from the saccule, so that in this way 

 the cavity of the saccule is brought into communication with that of the utricle 

 (Boettcher). Lastly, the saccule is connected with the membranous canal of the 

 cochlea by means of a short, narrow canal, the canalis rcunicns (Hensen). 



Semicircular Canals. — The membranous semicircular canals 



are about one-third the diameter of the osseous tubes in which they are 

 lodged, and are dilated into ampulte within the ampullary enlargements 

 of those tubes. In section they are oval or somewhat elliptical (fig. 



FiK. 459. 



Fi" 460. 



Fig. 459. — Membranous Labyrinth and Nervous Twigs detached, magnified (Breschet) 



k, facial nerve in the meatus aucUtorius internus ; I, anterior division of the auditory 

 nerve giving branches, o, m, n, to the utricle and the ampullfe of the superior and 

 external canals ; q, posterior division of the auditory nerve, giving branches to the 

 saccule, b, posterior ampuUa, c, and cochlea, r ; d, the united part of the superior and 

 posterior canals. 



Fig. 4C0. — Ahpull.e of the Superior and External Semicircular Canals and 

 Part of the Common Sinus, showing the Attachment op the Nerves (from 

 Steifensand). ^J-' 



1, membranous ampulla of the superior canal ; 2, that of the external canal ; 3, part 

 of_ the common sinus ; 4 and 5, forkdike swellings of the nerves at their ampullar dis- 

 tnbutiou ; 6, twig of the auditory nerve spreading in the common sinus. 



