408 



SPECIAL HISTOLOGY. 



Fig. 309. 



a 



former is developed at d, as an immediate 

 continuation of the periosteum of the lamina 

 spiralis ossea, and, in fact, only from that por- 

 tion of it which looks towards the scala vesti- 

 buli, increasing in width and thickness from the 

 commencement to the termination of the coch- 

 lear canal. In the first and second turns of the 

 cochlea, its under surface supplies the place of 

 the periosteum upon the most external portion of 

 the osseous zone, whilst in the last half turn it 

 is bounded only by the expansion of the nerve, 

 so that the habenula sulcata, in the strict sense 

 of the word, properly constitutes, in this situa- 

 tion, only a part of the so-termed membranous 

 spiral lamina. On the upper surface of this layer, 

 and on the outer border of it, there is an un- 

 interrupted series of clear, peculiarly glistening, 

 elongated, slightly clavate processes (g), the 

 "teeth" as they are termed (( ofthe first series" 

 which, in the first spiral turn of the cochlea, 

 are 0004 — 0-005'" wide, and 0-003'" thick, at 

 their origin, whilst in the last turn they are 

 not more than 0015'" long and 0-003'" broad. 

 They project, free, into the scala vestibuli, and 

 arch over the commencement of the habenula 



Fig. 309. Vertical section of the lamina spiralis, at 6"' 

 from its commencement, x circa 225 diam. (Cat or Dog) ; 

 the epithelial layer investing its upper and lower surfaces 

 is removed : a, periosteum of the osseous zone ; b, the two 

 lamellae of the osseous zone near its free border ; c, c', e", 

 termination of the auditory nerves ; d-w, lamina spiralis 

 membranacea ; d-w, zona denticulata; d-d'-f, habenula sulcata; d, place where 

 the periosteum is thickened ; e, granules in the groove of the habenula sulcata ; 

 f-ff, "teeth of the first series ;" g-f-h, sulcus s. semicanalis spiralis; h, its inferior 

 wall; k, epithelial cells at the entrance of the sulcus spiralis; h-w', habenula 

 denticulata; h-m, apparent teeth ; n-t, "teeth of the second series ;" n-p, their pos- 

 terior joint ; o, nucleated enlargement upon them ; p-q and q-r, articular portions ; 

 r-t, anterior joint of the second row; sss, three cylinder-cells, placed upon them; 

 l-v, membrane covering the habenula denticulata ; u, one of the epithelial cells under- 

 neath; w'-w, zona pectinata; x, periosteum, attaching the lamina spiralis (muse. 

 cocJilearis, Todd and Bowman) ; y, vas spirale internum ; z, its inner coat. After 

 Corti. 



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