ORGANS OF SPECIAL SENSE. 369 



Semicircular Canal*. These are three membranous tubes 

 corresponding exactly in shape, number, and form to the bony 

 canals in which they are contained. They are surrounded every- 

 where with perilymph, except at the ampulla?, where they are 

 in contact with the bony canals. The inner, or. epithelial layer 

 of the membrane in the ampullae, is covered with columnar 

 ciliated epithelium auditory hairs. 



Tin: MKM BRANOUS COCHLEA begins at the base and ascends 

 in a spiral course within the osseous cochlea to terminate in the 

 cupola. It includes only the canalis cochleae a part of the scala 

 vestibulae. As before stated, the membrana basilaris extends 

 from the margin of the lamina spiralis ossea to the outer wall of 

 the cochlea, dividing the cavity into the two scala 1 the scal;e 

 vestibule above, the scake tympani below. The former is again 

 subdivided by the membrane of Eiessner into two parts, the outer 

 of which forms the canalis cochlea, or scala media the mem- 

 lira nous cochlea proper on the floor of which is the organ of 

 Corti covered by the membrana tectoria. The scalar are lined 

 with periostium, and filled with perilymph. The scala tym- 

 pani ends at the fenestra rotunda, but the scala vestibula com- 

 municates freely with the vestibula. 



Limbus lamina', s/iini/i.^ is the periosteal margin of the 

 lamina spiralis ossea, and consists of an upper lip the labinm 

 rt'xlihnlare and a lower lip the labium tympanicum sepa- 

 rated by a groove the sulcus ,s/>m///x. 



d 



extends from the labium tympanicum 

 to the outer cochlear wall, to which it is attached by the liyn- 

 mentum spirale of Henle. 



Membrane of Reissner arises from the middle of the vestibu- 

 la r lamina and passes obliquely at an angle of 40 to the outer 

 cochlear wall, separating the canalis cochleae from the scala 

 vestibula. 



Canalis cochlea extends as a spiral sac closed at both ends 

 through the osseous cochlea, and contains the most important 

 part of the labyrinth the ultimate distribution of the auditory 

 nerve in the organ of Corti. It is triangular on section, the 

 membrana basilaris forming the base, the membrane of Jiiessner 

 the inner side, and the periosteum of the cochlea its outer side. 



Membrana tectoria, or membrane of Corti, commences as a 

 delicate membrane, at a point between the origin of the mem- 

 brane of Iiiessner and the- labium vestibule, and arches over to 

 the outer cochlear wall, inclosing the organ of Corti, but not in 

 contact with it. 



OKCAN OF CORTI consists of two sets of pillars the inner 

 and outer rods of Corti extending upward upon the vestibular 



