COCHLEA. 



385 



The "ligaments" of the ducts, the thin periosteum of the bony semi- 

 circular canals, and the perilymph spaces lined with mesenchymal epithe- 

 lium are seen in Fig. 431. 



COCHLEA. 



The relation between the ductus cochleae and the scalae tympani and 

 vestibuli is shown in Fig. 435. The ductus is triangular in cross section, 

 being bounded on its peripheral surface by the thick periosteum of the 

 bony wall of the cochlea; on its apical surface (toward the cupula) by the 

 membrana vestibularis [Reissner's membrane]; and on its basal or medial 

 surface by the lamina spiralis. These three walls may be described in turn. 



The peripheral wall of the cochlear duct is formed by the dense fibrous 

 periosteum attached to the bone, together with a large mass of looser tissue 



Blood vessels. 



Membrana 



Scala vestibuli 



Ductus 

 >--' cochlearis. 



' rf*" Vas prominens 



Ligamentum 

 spirale. 



Ganglion spirale. 



Scala tympani. 



Lamina spiralis ossea. Lamina spiralis membranacea. 



FIG. 435. THE PORTION OP FIGURE 432 MARKED "SCALA VESTIBULI" AND "SCALA TYMPAXI." X 50. 



crescentic in cross section, the ligamentum spirale (Fig. 435), The spiral 

 ligament is covered by a layer of cuboidal epithelial cells belonging to the 

 cochlear duct. Close beneath the epithelium there are blood vessels which 

 are said to give rise to the endolymph. The thick plexus which they form 

 is described as a band, the stria vascularis, which terminates more or less 

 distinctly with the vas prominens. The latter occupies a low elevation 

 of tissue which has its maximum development in the basal coil of the 

 cochlea (Fig. 435). 

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