368 MICROSCOPIC ANATOMY OF THE ORGANS. 



thin membrane, which is a process from the periosteum of the 

 scala vestibuli. It therefore consists of a thin connective-tissue 

 layer covered on the upper surface with flat cells, and on the 

 side toward the ductus with a single layer of flat polygonal 

 epithelial cells. 



The outer wall lies directly on the periosteum. The outer 

 layer, which consists of loose connective tissue, fuses with the 

 periosteum and forms together with this the ligamentum 

 spirale. From this, two processes extend toward the lumen of 

 the ductus cochlearis : the prominentia spiralis, which contains 

 a vein, the vas prominens ; and the so-called crista basilaris. 

 Between these processes there is a depression, the sulcus spiral)* 

 externus. The outer layer of loose connective tissue imme- 

 diately under the epithelium contains a dense network of blood- 

 vessels (stria vascularis). It reaches from the insertion of the 

 membrana vestibularis to the prominentia spiralis. Its capil- 

 laries play an important role in the secretion of the endolymph 

 of the cochlea. They are situated so close to the surface that 

 they enter the epithelial layer, and we have here to do with a 

 vascularized epithelium. The cubical epithelium covering the 

 stria vascularis is not sharply marked off from the connective 

 tissue. At the prominentia the epithelial cells are much lower 

 than elsewhere. They increase in height below, and pass over 

 into the cylindrical cells of the lamina basilaris. 



While the upper and outer are comparatively simple, the 

 lower (tympanal) wall shows a very complicated structure 

 (Fig. 270). It is formed partly by the limbus spiralis, which 

 rests on the free border of the lamina spiralis, and partly by 

 the lamina spiralis membranacea. 



The limbus is connected closely with the periosteum of the 

 underlying lamina spiralis ossea. It shows on its surface more 

 or less irregular papilla-like protuberances, and at the top of 

 the labium vestibulare a. series of radially arranged plates, the 

 so-called Huschke's auditory teeth. The entire surface of the 

 limbus is covered with a layer of cubical epithelial cells. At 

 the free border there is in the lamina spiralis ossea a series of 

 oval holes, the foramina nervina, through which the bundles 



