THE UTRICLE AND SACCULE. 235 



lining is thin ; in the lower or pharyngeal portion it is thicker, 

 underlaid with areolar submucous tissue, and contains mucous 

 glands and lymphoid tissue. 



The internal ear (or labyrinth) contains the terminal appa- 

 ratus of the auditory nerve, and occupies a tortuous bony 

 cavity (the " bony labyrinth") in the temporal bone. 



The bony labyrinth has three divisions the cochlea, semi- 

 circular canals, and vestibule, the latter connecting the two 

 others. 



Within the bony labyrinth is a membranous sac, the " mem- 

 branous labyrinth" containing " endolymph" and correspond- 

 ing in general to the windings of the bony labyrinth. 



The membranous labyrinth is separated from the bony 

 walls in most places by a peripheral lymph-space, lined with 

 endothelium and filled with "perilymph." 



The bony labyrinth is lined with periosteum, covered in 

 general with endothelium. 



The membranous labyrinth consists of the utricle and 

 saccule, situated in the vestibule, the membranous semicircular 

 canals, and the scala media of the cochlea. 



The neuro-epithelial terminals of the auditory nerve are 

 situated on the inner surface of the membranous labyrinth, 

 and consist of the maculce acusticce of the utricle and saccule, 

 the cristce acusticce of the ampullae of the semicircular canals, 

 and the organ of Corti. 



The vestibule is a bony chamber connecting the semicircular 

 canals with the cochlea. It contains the utricle and saccule, 

 which are separated from the bony walls by the perilymph- 

 space. This space is in relation with the middle ear by the 

 fenestra ovalis, which is closed by the base of the stapes. 



The utricle and saccule are rounded membranous sacs, com- 

 municating with each other by a small indirect canal, the 

 " ductus endolymphaticus." Their walls are formed by a 

 fibrous membrane lined internally with simple squamous epi- 

 thelium, altered to columnar in the maculae acustica3 ; exter- 

 nally they are covered with endothelium. They are connected 

 with the periosteum of the bony walls by fibrous bands, which 

 cross the peri lymph-space and convey vessels and nerves. 

 The utricle opens into the semicircular canals; the saccule 

 communicates through the small " canalis reuniens" with the 



