220 VISCERAL ANATOMY. 



f Utricle. 



Membranous Labyrinth, comprises the J Memb Semicircular Canal* 



j Saccule. 

 [ Membranous Cochlea. 



Auditory Nerve, the 8th cranial nerve, or the Portio Mollis of the 7th. 



Organ of Corti, the terminal auditory apparatus. 



Internal Auditory Canal. by which the auditory nerve enters. 



Describe the general arrangement of the Internal Ear. It lies in- 

 ternal to the tympanum, within the petrous portion of the temporal bone, and 

 consists of a series of osseous chambers, the Osseous Labyrinth, containing a 

 fluid, the Perilymph, or Liquor Cotunnii, in which lies a membranous repro- 

 duction of the chambers, the Membranous Labyrinth, which also contains a 

 fluid, the Endolymph, or Liquor Scarpa. Upon the membranous labyrinth 

 are distributed the terminal filaments of the auditor/ nerve, which being sus- 

 pended between two fluids, are not only protected from injury, but enabled to 

 perceive the most delicate vibrations which may be communicated to the fluids 

 surrounding them. 



Describe the Vestibule. It is the common cavity of communication 

 between the osseous parts of the internal ear, and measures in vertical diameter 

 about \ inch, laterally about ^ inch. It communicates in front with the scala 

 vestibuli of the cochlea; and behind (by five openings) with the semicircular 

 canals. It presents the following points, viz. : the 



FlG Io8 Fenestra Ovalis, on its outer wall, 



closed by the base of the stapes and 

 its annular ligament. 

 Fovea Hemispherical a small circular 

 depression on the inner wall, for the 

 saccule. 



Macula Cricosce, are groups of very 

 minute orifices on the inner wall, ad- 

 mitting the nerve filaments. 

 Crista, or Pyramidal Eminence, -a 

 vertical ridge on the inner wall, 

 bounding the fovea posteriorly. 



Aqueductus Vestibuli,d opens behind the crista, ending on the posterior 

 surface of the petrous portion of the temporal bone. It contains a small 

 blind canal opening by two arms, one into the utricle, the other into the 

 saccule ; also a small vein. 

 Fwea Semi-ellipticap a small oval depression on the roof, above and be- 



