134 THE AUDITORY NERVE AND COCHLEA, BY W. WALDEYER. 



a partly osseous and partly cartilaginous septum, the lamina spi- 

 ralis, which divides externally into two laminae that pass to 

 the osseous walls of the cochlea, and enclose the ductus coch- 

 learis between them (fig. 320, L Sp). In this way the osseous 

 canal of the cochleais divided by the ductus cochlearis and its two 

 attachments the osseous at the modiolus, and the membranous 

 towards the outer wall into two chambers, the scala tympani 

 (ST), and the Scala vestibuli ($F), which only communicate 

 with one another at the cupola of the cochlea by a fine aperture, 

 the helicotrema of Breschet. The scala tympani terminates 

 crecally, being cut off by the membrane of the fenestra rotunda 

 from the tympanic cavity; the scala vestibuli communicates 

 directly with the perilymphatic space of the vestibular sac- 

 culus. The situation of the ductus cochlearis in the cochlear 

 mass corresponds therefore to the semicircular canals and sac- 

 culi in the other part of the labyrinth (see the preceding 

 chapter). Like these, it is attached excentrically to the exter- 

 nal wall of the canal, and indeed by its opposite sides. 



The median lamina of attachment, (with reference to the 

 axis,) which at the same time supports the nerves, is here very 

 much elongated and ossified (lamina spiralis ossea) ; the lateral 

 lamina of adhesion, which especially supports the vessels (fig. 

 320, the connective tissue between h and b ; figs. 321 and 322, 

 e e), forms a thick cushion of connective tissue, which is semi- 

 lunar on section (ligamentum spirale, Kolliker). See below. 



The ductus cochlearis (fig. 320, e e 4 ; figs. 321 and 322, D (7) 

 forms in adults a tubular cavity, which is triangular in section, 

 and is enclosed by a connective-tissue membrana propria ; 

 towards the tympanum it is bounded by the membrana 

 basilaris (f L sp\ which is continuous with the crista spiralis 

 (E Or, figs. 321 and 322), in the sulcus spiralis internus 

 (S. sp. i), (the entire tympanal wall is included between 

 the letters E and L sp,) towards the vestibule, by the mem- 

 brane of Eeissner (f f, fig. 320; E R lt fig. 321); laterally 

 it is bounded by a vascular layer of connective tissue, which is 

 continuous with the periosteum .of the cochlea by means of 

 the above-mentioned semilunar cushion of connective tissue 

 (e e, figs. 321 and 322). Towards the inner side the membrana 

 Reissneri and crista spiralis join at a more or less acute angle. 



