472 



HISTOLOGY 



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. 477). 



The apical wall, or membrana vestibularis, consists of a thin layer of 

 connective tissue bounded on one side by the mesenchymal epithelium 

 of the scala vestibuli, and on the other by the simple flattened ectodermal 

 epithelium of the cochlear duct. 



Blood vessels. 



Labium 



Membrana 



Ganglion spirale. 



Scala vestibuli. 



Ductus 

 cochlearis. 



Vas prominens 



Ligamentum 

 spirale. 



Scala tympani 



Lamina spiralis ossea 



Lamina spiralis membranacea. 



FIG. 477. THE PORTION OF FIGURE 474 MARKED "SCALA VESTIBULI" AND "SCALA TYMPANI." X 50 



The basal wall or lamina spiralis extends outward from the modiolus 

 to the bony wall of the cochlea. Near the modiolus it lies between the 

 two scalae, but peripherally it is between the cochlear duct and the scala 

 tympani. Toward the modiolus it contains a plate of bone perforated 

 for the passage of vessels and nerves; this part is the lamina spiralis ossea. 

 The peripheral portion is the lamina spiralis membranacea. Both parts 

 are covered below by the mesenchymal epithelium of the scala tympani, 

 and above by the epithelium of the cochlear duct, including its complex 

 neuro-epithelium known as the spiral organ (of Corti). 



Where the membrana vestibularis meets the osseous spiral lamina, there 

 is an elevation of tough connective tissue called the limbus spiralis (Fig. 

 477). It consists of abundant spindle-shaped cells, and blends below with 

 the periosteum of the spiral lamina. Superficially it produces irregularly 



