THE EAR ,553 



lymph, which is continuous with the periI>Tnph of the vestibule 

 ^srA osseous semicircular canals. The scala media contains endo- 

 lymph, which is continuous with that of the saccule. 



Basilar Membrane. — The basilar membrane extends from the 

 iree margin of the lamina spiralis to the crista basilans, or lower 



Modiolas 

 Osseous Spiral T^'" '"» ''^^^SS^jfes Scala V'estibuli 

 Membrane of Reissner .^^3=i^^2 ^^^S^^ Scala Media 



Basilar Membrane >^5 ^nV',?! ; .: ^-^ala Tympani 



Fig. 652. — Vertical Section of the Cochlea of a F<etal Calf, showing 



THE SCAL^ AND MODIOLUS (KoLLIKER). 



part of the spiral ligament, which ligament is a thickening of the 

 periosteum of that part of the outer wall of the cochlea which forms 

 the outer wall of the scala media, or ductus cochlearis. It separates 

 the scala media from the scala tympani, and is divisible into two 

 zones, inner and outer. The inner zone is called the zona arcuata, 

 and it supports the organ of Corti. The outer zone is called the 

 zona fectinata, and it extends from the foot-plates of the outer 

 rods of Corti to the crista basilaris. The basilar membrane consists 

 of a homogeneous membrana propria, with fibres embedded in it, 

 the fibres being most numerous in the zona pectinata. 



Membrane of Reissner. — ^This is a delicate membrane which ex- 

 tends from the upper surface of the lamina spiralis, a short distance 

 from its free margin, to the outer wall of the cochlea, where it is 

 attached to the periosteum at a point a short distance above the 

 outer attachment of the basilar membrane. It separates the scala 

 media from the scala vestibuli, and consists of a very delicate 

 connective-tissue membrane, lined on each side with a single layer 

 of squamous epithelium. 



The scala media, or ductus cochlearis, is situated between the 

 basilar membrane and the membrane of Reissner. It is triangular 

 in transverse section, and presents a roof, an outer wall, and a 

 floor. The roof is formed by the membrane of Reissner, which, 

 as just stated, separates the scala media from the scala vestibuli. 

 The outer wall is formed by the outer wall of the cochlea and its 

 periosteum, between the external attachments of the basilar 

 membrane and the membrane of Reissner. The periosteum in 

 this region is much thickened, and forms the spiral ligament of the 

 cochlea, the lower part of which gives rise to the crista basilaris. 

 The floor is formed by 11) the basilar membrane, and (2) the 

 portion of the upper surface of the lamina spiralis which lies ex- 

 ternal to the attachment of the membrane of Reissner. As stated, 

 i:he basilar membrane separates the scala media iroia. the scala 



.■ >n<i70D DBS nt 



