8io 



MEMBRANA RETICULARIS. 



the beams of a house. But every two rods do not form an arch as there are always three inner 

 to two outer rods {Claudius). There are about 4500 outer rods (Waldeyer). 



The duetus cocnlearis becomes larger towards the apex of the cochlea, and the rods also 

 become longer ; the inner ones are 30 M long in the first turn and 34 M in the upper the 

 outer rods 47 M and 69 M respectively. The span of the arches also increases (ffensen). [The 



Scheme of the ductus cochlearis and the organ of Corti. N, cochlear nerve; K, inner, and P, 

 outer hair-cells; n, nerve-fibrils terminating in P; a, a, supporting cells; d, cells in the 

 sulcus spiralis; z, inner rod of Corti; Mb. Corti, membrane of Corti, or the membrana 

 tectoria; o, the membrana reticularis; H, G, cells filling up the space near the outer wall. 



arches leave a triangular tunnel beneath them.] The proper end-organs of the cochlear nerve 

 are the cylindrical "hair-cells" (Kolliker) previously observed by Corti, which are from 

 16,400 to 20,000 in number (Hensen, Waldeyer). There is one row of inner cells (t), which 

 rests on a layer of small granular cells (K) (Butcher, Waldeyer) ; the outer cells (a, a) number 

 12,000 in man (Retzius), and rest upon the basement membrane, being disposed ;in three or 

 even four rows. Between the outer hair-cells there are other cellular structures, which are 

 either regarded as special cells (Deiter's cells), or are regarded merely as processes of the hair- 

 cells (Lavdowsky). [The cochlear branch of the auditory nerve enters the modiolus, and runs 

 upwards in the osseous channels there provided for it, and as it does so gives branches to the 

 lamina spiralis, where they run between the osseous plates which form the lamina.] The 

 fibres (N) come out of the lamina spiralis after traversing the ganglionic ceUs in their course 

 (figs. 591, 595, I, G), and end by fine varicose fibrils in the hair-cells (fig. 595) ( Waldeyer, 

 Oottstein, Lavdowsky, Retziiis). 



Membrana Reticularis. Corti's rods and the hair-cells are covered by a special membrane 

 (o), the membrana reticularis of Kolliker. The upper ends of the hair-cells, however, project 

 through holes in this membrane, which consists of a kind of a cement-substance holding these 

 parte together {Lavdowsky). [Springing from the outer end of the lamina spiralis, or crista 

 spiralis, is the membrana tectoria, sometimes called the membrane of Corti. It is a* well- 

 defined structure, often fibrillated in appearance, and extends outwards over the organ of Corti] 

 Waldeyer regards it as a damping apparatus for this organ (fig. 595, Mb. Corti). 



[Basilar Membrane. Its breadth increases from the base to the apex of the cochlea. This 

 fact is important in connection with the theory of the perception of tone. It is supposed that 

 high notes are appreciated by structures in connection with the former, and low notes by the 

 upper parts of the basilar membrane. In one case, recorded by Moos and Steinbrugge, a 

 patient heard low notes only in the right ear, and after death it was found that the auditory 

 nerve in the first turn of the cochlea was atrophied. ] 



Intra-Labyrinthine Pressure. The lymph within the labyrinth is under a certain pressure. 

 Every diminution of the pressure of the air in the tympanum is accompanied by a correspond- 

 ing diminution of the intra-labyrinthine pressure, while conversely every increase of pressure 

 is accompanied by an increase of the lymph -pressure (F. Bczold). 



