ORGANS OF THE BODY. 



659 



...-E 



...J7 



covered underneath, but not above, with a single layer of epithelium. 

 The outer wall of the canalis cochlearis is likewise formed by a coat of 

 periosteum overlaid with similar cells (&'). In it, also, may be recognised 

 a peculiar eminence (m), a layer of cartilage situated higher up (n), and a 

 vascular streak (0). 



The floor of the canalis cochlearis, i.e., the upper surface of the lamina 

 spiralis membranacea, exhibits a very complex structure ; while the under 

 surface, or that facing the scala tympani, presents nothing remarkable for 

 our consideration, with the 

 exception of the so-called 

 vas spirale (b), enveloped 

 in a thin coating of connec- 

 tive-tissue. 



The very important struc- 

 tures to be seen here were 

 in part discovered by Corti, 

 who was succeeded by Reiss- 

 ner, Claudius, Bottcher, 

 Scnultze, Deiters, Koelliker, 

 and Hensen (without men- 

 tioning many others), by 

 whom the wonderful ar- 

 rangement of parts was 

 further and further un- 

 veiled, at the same time 

 that its complexity was ren- 

 dered so evident as to 

 baffle all hopes of arriv- 

 ing at anything like de- 

 finite conclusions for the 

 present. 



According to Corti, the 

 membranous spiral plate 

 may be divided into two 

 zones, an internal zona 

 denticulata, and an external 

 z. pedinata (<?). 



The zona denticulata has 

 been again subdivided into 

 two portions, namely, into 

 the habenula internet, or sul- 

 cata (c), or labium superius 

 of the sulcus spiralis, and 

 into the h. externa, s. den- 

 ticulata (e, h). 



The first of these presents 

 itself as a high eminence, 

 the crista spiralis, project- 

 ing into the canalis coch- 

 learis with comb-like ridges 



... A 



Fig. 607. The organ of Corti from the dog, after Waldeyer. 

 seen on its vestlbular aspect, the membrane of Reissner 

 and the so-called membrana tectoria having been removed. 

 A, Crista spiralis ; B, epithelium of the sulcus spiralis; C, 

 pillar heads of the fibres of Corti; D, lamina reticularis; 

 E, external epithelium of the membrana basilaris ; a, cells 

 of the sulcus spiralis shining through the acoustic teeth; 6, 

 corresponds to the outer boundary line of these teeth ; e, 

 cuticular meshwork between the internal epithelial cells; 

 d, vas spiral! ; e, internal hair cells; /, heads of the inter- 

 nal pillars, or fibres of Corti; fi, their head plates; g, 

 boundary line between the external and internal pillars ; 

 /, heads of the external pillars shining through the head 

 plates of the internal fibres of Corti (the clear circle is the 

 optical transverse section of the external fibre or pillar) ; I, 

 phalangcal head-plate of the external pillar or the first 

 phalanx ; k, m, o, first, second, and third rings of the lamina 

 reticularis, with the hairs or filaments of the first, second, 

 and third rows of hair or tufted cells; n and p are the 

 second and third phalanges ; r, supporting cells (Hensen) ; 

 g, cuticular network between the epithelial cells or the 

 framework of Deiters. 



and grooved external bor- 

 der. The furrow is known as the semicanalis or sulcus spiralis (d). 

 The whole structure results from the peculiar disposal of the periosteum 



