THE BASILAR MEMBRANE, 



117 



to Retzius, 33'5 mm. The basilar membrane is usually described as showing two 

 zones, viz., the zona arcuata, which is the part upon which the rods of Corti stand, 

 and the zona pectinata, extending from the feet of the outer rods to the spiral liga- 



Fig. 133. BASILAR MEMBRANE AND LIMBUS VIEWED 

 FROM ABOVE. Magnified. (GK Retzius.) 



ment, the latter zone being somewhat thicker 

 and much more distinctly fibrous. The proper 

 substance of the membrane appears to be 

 formed of a homogeneous ground-substance 

 containing nuclei embedded in it here and 

 there, and having straight fibres (running 

 radially from the spiral lamina to the external 

 spiral ligament) embedded in it, so that the 

 membrane, especially its outer part, presents 

 a marked striation when viewed on the sur- 

 face (fig. 133). Externally, at its attachment 

 to the spiral ligament, it breaks up into 

 diverging fibres, which spread into that pro- 

 jection. In a section of the membrane across 

 the direction of its fibres the latter appear as 

 fine points enclosed by the homogeneous 



^Ucurwrbcb 



Fig. 134. TANGENTIAL SECTION ACROSS THE ZONA 



PECTINATA OP THE BASILAR MEMBRANE OF THE 



GUINEA-PIG. (Schwalbe. ) Highly magnified. 



ground-substance (fig. 134). In chemical 

 nature they resemble elastic fibres but are 

 rather less resistant to alkalies and most other 

 reagents. It has been calculated by Retzius 

 that there are altogether as many as 24,000 of 

 these fibres in the human membranabasilaris, 

 but they do not all run singly, some being 

 top-ether. On the unner surface of the 



To go opposite p. 116.] 



In the description of fig. 132 the words "In the lower half- in the osseous substance," 



are to be omitted ; and in the last line of the description the words " cells of Deiters " are 

 to be substituted for "outer hair-cells " 



of the membrane), the fibres of which have a 

 direction parallel with the spiral, and across 

 that of the fibres of the membrane proper. 

 There are numerous intermixed spindle- 

 shaped corpuscles in this tissue, which is in 

 continuity with the lining periosteum of the 

 scala tympani (fig. 134). Small blood-vessels 



are found in it, but as a rule extending only over the inner part of the membrane. 

 They are usually terminated by a rather larger longitudinally running vessel, 

 situated opposite the outer rods o!' Corti, and known as the vas spirals (fig. 136). 



