582 



THE ORGANS 



lose their medullary sheaths and split up into several small branches, 

 which form a horizontal plexus between the basement membrane and 

 the bases of the hair cells. From this plexus are given off fibrils 

 which end freely between the hair cells. 



Semicircular Canals. — The walls of the semicircular canals are 

 similar in structure to the walls of the saccule and utricle; they also 

 bear a similar relation to the walls of the bony canal. Along the con- 

 cavity of each canal the epithelium is somewhat higher, forming the 



Fig. 3S6. — Diagram of the Perilymphatic and Endolymphatic Spaces of the Inner 

 Ear. (Testut.) Endolymphatic spaces in gray; perilymphatic spaces in black, i, 

 Utricle; 2, saccule; 3, semicircular canals; 4, cochlear canal; 5, endolymphatic duct; 6, 

 subdural endolymphatic sac; 7, canahs reuniens; 8, scala tympani; 9, scala vestibuli; 

 ID, their union at the helicotrema; 11, aqueduct of the vestibule; 12, aqueduct of the 

 cochlea; 13, periosteum; 14, dura mater; 15, stapes in fenestra ovalis; 16, fenestra 

 rotunda and secondary tympanic membrane. 



raphe. In each ampulla is a crista aciistica, the structure of which is 

 similar to that of the maculae of the saccule and utricle. With the 

 adjoining high columnar cells, this forms the so-called semilunar fold. 

 As in the case of the macular the hair cells have otoliths upon their 

 surfaces, the otohthic membrane here forming a sort of dome over the 

 hair cells known as the cupula. 



The Cochlea. — The bony cochlea consists of a conical axis, the 

 modiolus, around which winds a spiral bony canal. This canal in 

 man makes about two and one-half turns, ending at the rounded tip 

 of the cochlea orcupola. Projecting from the modiolus partly across 



