222 VISCERAL ANATOMY. 



the membranous cochlea, into 2 Scalae, the Scala Vestibuli^ and the 

 Scala Tympani. n [Fig. in.] 



[A third scala is described by many authorities, the Scala Media, 9 including 

 the space occupied by th'e membranous cochlea. See Fig. 1 1 1.] 



Describe the Scala Vestibuli. It is the portion of the spiral canal lying 

 above the lamina spiralis and the membranous cochlea ; communicates with 

 the vestibule below, and with the scala tympani above at the Helicotrema. It 

 is filled with perilymph. 



What is the Scala Tympani ? It is the portion of the spiral canal lying 

 below the lamina spiralis and the membranous cochlea, communicates with 

 the aqueductus cochlea (see below), and with the scala vestibuli at the Heli- 

 cotrema. It terminates inferiorly at the fenestra rotunda, and is rilled with 

 perilymph. 



What is meant by the Helicotrema ? It is a space at the apex of the 

 cochlea, formed by the deficiency of the lamina spiralis in the last half turn 

 of the same. In this space the two scabe are believed to open, thereby 

 communicating with each other. 



What is the Aqueductus Cochleae ? A small canal which begins by a 

 small orifice in the lower wall of the scala tympani, and runs in the inner wall 

 of the jugular fossa, ending at the edge between the inferior and inner surfaces 

 of the petrous portion of the temporal bone. It transmits a vein from the 

 cochlea to the jugular vein. 



What Parts are comprised in the Membranous Labyrinth? It 

 consists of two membranous sacs, the Utricle^ and Saccule, * which lie in 



the vestibule, together with the Membranous 



FIG. no. Semicircular Canals,* and the Membranous 



Cochlea.*, 5 The utricle and saccule com- 

 municate with each other indirectly by a 

 small canal contained in the aqueductus 

 vestibuli. The saccule communicates with 

 the membranous cochlea by the Canalis Re- 

 uniensf and the membranous semicircular 

 canals open into the utricle; so that the 



membranous labyrinth presents an uninterrupted channel for the endolymph 

 which it contains. 



What is the Utricle ? It is a flattened, elliptical membranous sac, fastened 

 to the inner wall of the vestibule in the fovea semi-elliptica. It is filled with 

 endolymph, nearly surrounded by perilymph, and communicates with the 

 saccule through the small tube in the aqueductus vestibuli. The membranous 



