764 THE EAR. 



Fig. 521. 



Fig. 521. UPPER OR YESTIBULAR SURFACE OF A NARROW STRIP OF THE LAMINA 

 SPIRALIS MEMBRANACEA (from Kolliker after Corti). 2 -p 



The drawing is defective as regards the organ of Corti, but explains the nomenclature 

 of the parts introduced by that author, and more or less adhered to by subsequent writers, 

 although variously departed from in some of its details. The nomenclature adopted in the 

 text has been selected from various writers, and it will be observed difiers considerably 

 from the following : a, periosteum of the zona spiralis ossea ; d w, lamina spiralis mem- 

 branacea ; d w', zona denticulata ; d f, habenula sulcata ; d, place where the perios- 

 teum thickens ; e, granules in the areolse of the habenula sulcata ; fg, teeth of the first 

 series; fffh, sulcus vel semicanalis spiralis; A, its lower wall ; h w, habenula denticu- 

 lata; Jim, apparent teeth ; nt, teeth of the second series ; np, inner segments of the 

 same; o, swellings with nuclei ; pq and qz, articulating pieces of the same : f, anterior 

 segments of the second series ; s s s, three cylindrical cells placed on them ; w, epithelial 

 cells placed under the membrane of Corti ; w' w, zona pectinata ; a a, band-like 

 elevations of the habenula sulcata ; #, placed where a tooth of the first series takes 

 its origin ; 7, holes between the apparent teeth ; 5, fore part of one of the teeth of the 

 second series thrown back ; e, one of them in its place without its epithelial cells ; one 

 with only the lowest epithelial cell ; i\, one with the two lowest cells ; 8, striae or slight 

 elevations of the zona pectinata ; /c, periosteum attaching the lamina spiralis, with A, 

 apertures between the bundles. 



the increasing breadth of the membrane from base to apex of the cochlea 

 is due to broadening of the zona pectinata. According to the same 

 observer the membrane is mainly homogeneous, and in the outer zone is 

 thicker than in the inner, and somewhat tuberculated ; but on the surface 

 towards the membranous canal it is transversely striated by a layer of 

 extremely delicate fibres ; and on the other surface is a less perfect layer 

 of fibres with spindle-shaped corpuscles, which are placed longitudinally, 

 and in young subjects are arranged so as to cover the inner zone and the 

 attachment to the spiral ligament, leaving the outer zone free. A single 

 layer of epithelium lies on the surface. 



The ligamentum spirale (musculus cochlearis of Todd and Bowman) is 

 triangular in section, receiving at its inner angle the basilar membrane, and 

 spreading out rapidly to be attached by a broad base to the wall of the 

 cochlea. Its fibres are directed outwards from the membrane to the bone, 

 and it exhibits nuclei, like the ciliary muscle, whence Todd and Bowman 

 conceived it to be muscular. Hensen represents it as composed of branch- 

 ing nucleated cells. 



The organ of Corti. Under this name may be comprised the whole of 

 the structures intervening between the membrana basilaris and meinbrana 

 tectoria. The most prominent part of it is formed by an outer and an inner 

 series of rods, which, attached respectively to the inner and outer margins of 

 the inner zone of the basilar membrane, meet together like the beams of a 

 roof, and cover in a three-sided space, of which the inner zone of the basilar 

 membrane is the floor. These structures, the fibres or rods of Corti, are 

 closely adherent by their lower extremities to the basilar membrane. They 

 are placed with the regularity of piano keys, and have been likened in con- 



