622 THE EAK 



are prolonged outward between the nucleated portions of the sus- 

 tentacular cells and frequently terminate in small knobbed extrem- 

 ities. This portion of the cells is in intimate relation with the ter- 

 minal fibrils of the vestibular nerve, which, coming from nerve 

 plexus in the fibrous wall of the saccule, forms an intra-epithelial 

 plexus of delicate varicose fibrils. Frequently the epithelial coat 

 contains coarse granules of a brownish pigment which, at times, 

 also produces a diffuse coloration of the cells. 



The epithelial coat of the saccule rests upon a thin homo- 

 geneous basement membrane and is further supported by a delicate 

 fibrous coat or tunica propria. The connective tissue of this coat 

 forms interlacing bundles the most of which are distributed in a 

 circular manner about the wall of the ovoid saccule. At the 

 macula this coat is much thickened by the entrance of the nerve 

 fibres from the vestibular nerve. It also contains the minute 

 blood vessels which supply the organ. 



As is the case with the other divisions of the membranous laby- 

 rinth, the fibrous wall of the saccule is in contact on one aspect of 

 its surface with the periosteum which lines the osseous labyrinth ; 

 elsewhere it is separated from the periosteum by the perilymphatic 

 cavity. 



The utricle is somewhat larger than the saccule. It lies behind 

 and somewhat above the saccule, is of a very irregular oblong form, 

 and receives the insertions of the semicircular canals. Its anterior 

 portion is provided with a macula and the structure of its wall 

 differs in no wise from that of the saccule; both of these mem- 

 branous sacs are contained within the irregular cavity of the vesti- 

 bule. The structure of the utricle, therefore, requires no further 

 description. 



The Semicircular Canals. The semicircular canals are three in 

 number, the posterior, superior, and external. The last is also 

 horizontal in its position ; the first two are vertical, but are so 

 placed as to form a right angle with one another. The superior 

 lies in the long axis of the petrous bone and its plane is therefore 

 more nearly coronal, while that of the posterior canal is more 

 nearly sagittal. Each canal forms something more than half a 

 circle, its two ends opening separately into the cavity of the vesti- 

 bule, with the exception of the posterior and superior canals whose 

 inserted ends open by a common orifice, the canalis communis. 

 The unjoined orifices of the posterior and superior canals, as also 

 the outer extremity of the external canal, present a marked dila- 



