THE INTERNAL EAR. 



48l 



The membranous labyrinth differs in shape from the osseous 

 labyrinth in that, in place of the single chamber (vestibule) of the 

 latter, the membranous labyrinth presents two sacs, the utriculus 

 and the sacculus, united by a narrow duct, the utriculosaccular 

 duct. The utriculus is the larger, and from it arise the membran- 

 ous semicircular canals. These present ampullae, situated within 

 the osseous ampullae previously mentioned. The sacculus com- 

 municates with the cochlear duct by means of the canalis reuniens 

 (Hensen). From the utriculosaccular duct arises the ductus 

 endolymphaticus, which passes through the aqueductus vestibuli 

 and ends in a subdural sacciis endolymphaticus on the posterior sur- 

 face of the petrous portion of the temporal bone. 



In the membranous labyrinth the nerves are distributed over 

 certain areas known as the maculce, cristce, and papilla spiralis. 



,' "i 



Auditory nerve 

 with its vestihu- 

 lar and cochlear 

 branches. 



Ant. semicircular canal. 

 Ampulla. 



Cochlear duct. Canalis reuniens. Ductus Ampulla. Horizontal semicir- 



endolymphaticus. cular canal. 



Fig. 369. Membranous labyrinth of the right ear from five-month human embryo (from 

 Schwalbe, after Retzius). 



There is a macula within the recess of the utriculus, the macula 

 acustica utriculi ; and another within the sacculus, the macula 

 acustica sacculi ; cristae are present in the ampullae of the upper, 

 posterior, and lateral semicircular canals, the cristce ampullares sup., 

 post., et lat. Besides these, we have the terminal arborization of 

 the acoustic nerve in the membranous cochlea, the papilla spiralis 

 cochlece, or the organ of Corti. 



3 



