AND THE CRISTA SPIRALIS OF THE COCHLEA. 79 



polygon of the superficial mosaic covering the crista spiralis. Each of them is for 

 the most part derived from one polygon of the mosaic of the greater ridge, but also 

 somewhat from a mesh of the secondary network covering one polygon of the crista 

 spiralis, which (according to all investigators) represents the least active segment 

 of the anatomical substratum. But it is impossible to give even an approximate 

 estimate of the exact parts played by these two substrata. 



I have been able to describe the genesis of an interprismatic substance between 

 the prisms produced by the greater ridge, but the genesis of similar spaces between 

 the portions of cylinders formed by the crista spiralis and by the membrana retic- 

 ularis of the organ of Corti is still obscure. If further investigation should con- 

 firm the existence of this kind of cement for the first segment and the lack of it in 

 the other two segments, this distinctive feature might enable other investigators 

 to determine accurately the parts of the prisms derived from each of the three 

 segments of the anatomical substratum. 



STRUCTURE OF THE ADULT MEMBRANA TECTORIA. 



Most authors distinguish three segments in the adult tectorial membrane: a 

 thin, innermost axial segment covering the crista spiralis; an outermost lateral, 

 derived from the lesser ridge; a thick middle segment produced by the greater 

 ridge according to the investigations of: Henle (1866), Lowenberg (1868), Boettcher 

 (1869), v. Winiwarter (1870), Gottstein (1870), Hensen (1871), Lavdowsky (1876), 

 Nuel (1878), Retzius (1884), Barth (1889), Dupuis (1894), Coyne and Cannieu 

 (1895), Held (1909), and Prentiss (1913). 



The middle segment is striated and the striations incline from the vestibular 

 lip toward the organ of Corti, the inclination being due to the existence of fibers or 

 of fibrils as stated by Hensen (1863), Henle (1866), Boettcher (1869), v. Winiwarter 

 (1870), Lavdowsky (1876), Nuel (1878), Tafani (1882), Retzius (1884), Ferre (1885), 

 Ranvier (1889), Barth (1889), Ayers (1891), Dupuis (1894), Hardesty (1908), 

 Held (1909), and Vasticar (1909). According to Coyne and Cannieu (1895), Sham- 

 baugh (1907), and Prentiss (1913), they are due to the presence of lamelke. Most 

 authors agree upon the presence of a homogeneous fluid between these constituents, 

 though Retzius denies it. 



The inner segment is described by Henle (1866), Boettcher (1869), v. Wini- 

 warter (1870), Hensen (1871), and Nuel (1878) as a more or less homogeneous but 

 fenestrated membrane provided with openings. Gottstein (1870) and Lavdowsky 

 (1876) regard it as structureless and without openings. Retzius (1884), Barth 

 (1889), and Dupuis (1894) consider it as formed by thin radiating fibrils which 

 according to Held are collected in bundles separating openings. The outer seg- 

 ment, as stated by Henle (1866), Boettcher (1869), v. Winiwarter (1870), Gottstein 

 (1870), Nuel (1878), Retzius (1884), Dupuis (1894), and Held (1909), consists 

 of a network of anastomosed fibrils, filaments, or hyalin bands. Hardesty (1908) 

 describes an accessory tectorial membrane as formed by two sets of fibers crossing 

 at an acute angle. 



