60 THE GENESIS AND STRUCTURE OF THE MEMBRANA TECTORIA 



on the surface of the somewhat thick epithelial layer covering the interior wall of 

 the ductus cochlearis next to the scala tympani. While the two epithelial ridges 

 and the crista spiralis are developing, the membrane thickens and is in close con- 

 tact with the surface of their superficial epithelium, which I consider as the gener- 

 ating substratum, the matrix of the membrane of Corti, according to the investi- 

 gations of most authors (Boettcher 1869, Nuel 1878, Pritchard 1876, Retzius 1884, 

 Denis 1901, Rickenbacher 1901, Held 1909). Others believe that the process of 

 formation extends farther over the surface of Hensen cells and Claudius cells 

 (Hensen 1871, Tafani 1882, Dupuis 1894, Coyne and Cannieu 1895, Czinner and 

 Hammerslag 1898, Vasticar 1909, Prentiss 1913). Previous authors asserted that 

 the membrana tectoria reaches and is attached to the ligamentum spirale (Corti 

 1851, Claudius 1855, Boettcher 1859, Henle 1866, Loewenberg 1868, Earth 1889). 

 Everyone who has studied this question has recognized that the greater ridge is the 

 most active segment of this substratum; the crista spiralis, at the surface of which 

 the membrane remains fixed in the adult cochlea, is of less significance; indeed, 

 its activity ceases before the stage of complete development of the organ of Corti. 

 A few authors, with Koelliker (1859), assert that the lesser ridge does not take part 

 in the formation of the membrane, and Vernieuwe (1905) and Hardesty (1908, 1915) 

 attribute very little importance to it. 



Most investigators concur in regarding the membrana tectoria as a cuticular 

 product of the cytoplasmic apices of the surface epithelial cells (Koelliker 1861, 

 Hensen 1863, Middendorp 1867, Rosenberg 1868, Winiwarter 1870, Gottstein 

 1870, Pritchard 1876, Nuel 1878, Retzius 1884, Coyne and Cannieu 1895, Denis 

 1901, Rickenbacher 1901, Vernieuwe 1905, Hardesty 1908, Vasticar 1909, Prentiss 

 1913); whereas some (Boettcher 1869, Ayers 1891, Czinner and Hammerslag 1898) 

 consider it to be produced by hairs, cilia, or filaments. Held (1909) practically 

 confirms this opinion. I must, therefore, consider the apices of the superficial 

 epithelium which enter into this process of genesis. 



THE GREATER AND LESSER EPITHELIAL RIDGES. 



On a transverse section of the tympanic wall of the cochlear duct, in the earliest 

 stages before the appearance of the crista spiralis (pig embryo 60 mm.), and later, 

 when the crista spiralis and the two rfdges are visible but before any trace of dif- 

 ferentiation has taken place in the sensorial elements, the wall of these regions is 

 lined by a rather thick epithelium which was regarded by certain earlier authors 

 (Koelliker 1859, Middendorp 1867, etc.) as formed by superposition of many rows 

 of cells. But Hensen (1863), Boettcher (1869), Baginsky (1886), and other more 

 recent investigators describe it as a simple columnar epithelium. The elongated 

 prismatic cells reach the inferior and superficial part of the layer and their nuclei 

 are situated at various heights. Figure 1, from a new-born dog, shows such a 

 section near the top of the cochlea, with the first indication of the greater ridge 

 (<//) and with the future lesser ridge (Ir) not yet prominent. A superficial mosaic 

 is visible at my, ml, on the two segments, but without any differentiation in the 

 sensorial fields. Many rows of nuclei (n) are apparent in the segment of the future 

 lesser epithelial ridge. 



