460 Dynamic Theory. 



bular, and distributes its fibres to the vestibule and the ampullae, while 

 the other runs up the center of the stem of the cochlea and is called the 

 cochlear nerve. This last sends fibres to receive the agitation of a very re- 

 markable set of organs found in the sac described above as the scala media. 



FIG. 196. Section of Cochlea of foetus of 

 Calf, from, top to bottom, cutting 1 across 

 the Scala Tympani, Scala Vestibuli and 

 Scala Media. Modiolus not yet ossified. 

 Organs of Corti begun. 



St. Scala Tympani. 



6. Basilar membrane holding Organs 

 of Corti. 



sv. Scala Vestibuli. 



v. Membrane separating the S. Media 

 from the S. Vestibuli. 



Scala Media lies between the membranes 

 6 and v. ( After Kolliker.) 



FIG. 196. 

 This, as before stated, is coiled around the stem of the Cochlea, having 



the scala vestibuli above and the scala tympani below it ; from each of 

 which it is separated by a membrane. The membrane which forms its 

 bottom is called the basilar membrane. The inner edge of the basilar 

 membrane is supported by a bony process which constitutes a portion of 

 the bony stem or modiolus, the hollow conical pillar around which the 

 three scalas gyrate like a three story stairway. The width of the basi- 

 lar membrane increases regularly from the bottom to the top. The 



FIG. 197. Diagram of the Basilar Membrane; the floor of th 



Organs of Corti. 

 a b d. Lower end of the stairs in which the arches of Corti are 



of shorter span. 

 a b' d' Upper end. 



(The membrane of an infant, measured by Hensen, was one- 

 fiftieth of an inch wide at the summit and one three-hundredth 

 at the lower end.) 



membrane is traversed from side to side by cross 

 fibres, in fact it is composed- of cross fibres laid 

 side by side in vast numbers. The remarkable organs 

 alluded to are called the organs of Corti. They con- 

 sist of a series of arches, each arch composed of two 

 fibres arranged to partly span across the basilar 

 membrane. The arches stand on, and are parallel FlG 197 



with the cross fibres of the membrane, probably one arch on each fibre. 

 The shape of the arches is shown in fig. 198. The left hand fibre, the 

 inner one, stands on the inner edge of the membrane next to the modi- 

 olus, the outer one rests not far from the middle of the membrane. 

 The two fibres are joined at the top to form the arch, and then turned 

 outward into a short prolongation, as shown in the figure. The span of 

 these arches regularly increases from the bottom to the top of the scala, 

 so that the upper arches have a greater span, though no greater rise, 

 than the lower ones. The number of the arches is about 4,000. 

 The space upon the basilar membrane not occupied by the arches is 



