162 



TOPOGRAPHICAL ANATOMY OF THE 



helicotrema^ through which the scala vestibuli and scala tympani 

 communicate with each other. 



Close to the fenestra cochlege there is a small opening leading into 

 the aquceductus cocJdecc, which traverses the temporal bone to open on 

 its cerebral surface posterior to the internal acoustic meatus. The 

 aqueduct places the scala tympani in communication with the subar- 

 achnoid space. 



llie Membranous Labyrinth (labyrinthus membranaceus). — The 

 membranous labyrinth consists of the utricle, the saccule, three semi- 

 circular ducts and the cochlear duct. The utricle - (utriculus) lies in 

 the upper and posterior part of the vestibule, part of it being accom- 

 modated in the recessus ellipticus. The saccule (sacculus), smaller than 

 the utricle, occupies the recessus spharicus of the vestibule. The 



Scala vestibuli. Vestibular membrane (of Reissner). 



Modiolus. 



Osseous spiral lamina. 

 Ganglion spirale. 



Cochlear duct. 



.Membrana tectoria. 



Lig. spirale cochlese. 

 Organ of Corti. 



Scala tympani. Basilar lamina. 

 Fig. 74. — Section across the cochlea. 

 ductus endolyiwpliaticus leaves its posterior part, and is joined by the 

 ductus utriculosaccidaris from the utricle. The endolymphatic duct 

 traverses the aquseductus vestibuli of the temporal bone, and ends 

 under the dura mater as a dilatation, the saccus endolymphaticus. 



The semicircular ducts (ductus semicirculares) lie within the 

 osseous semicircular canals, to the walls of which they are attached by 

 their convex borders. Each duct is ampullated at one end, in agree- 

 ment with the canal containing it. The non-ampullated ends of the 

 superior and posterior ducts are united, and consequently the three 

 ducts open into the utricle by five openings. 



The cochlear duct (ductus cochlearis) is attached on one side to the 



1 i\i^ (helix) [Gr.], a spiral, anything that assumes a spiral shai:)e. rpij/xa (trGnia) 

 [Gr.], a hole. 



2 Utriculus (dim. of uler) [L.], a small bag or bottle made of hide, a skin for 

 wine, &c. 



