THE INTEENAL EAE 705 



membrane; that which impinges upon the scala tympani slopes more 

 abruptly. The greater portion of the spiral ligament, therefore, is con- 

 tained within the scala media. Here it is lined by low columnar or 

 cuboidal epithelium whose cells blend, without demarcation, with the 

 underlying vascular connective tissue, so that the minute blood-vessels 

 frequently appear as if lying within the epithelial layer, although they 

 probably are always contained within the connective tissue processes 

 which project into the attached surface of the epithelial layer. 



This very vascular subepithelial portion of the spiral ligament is 

 known as the stria vascularis. A short distance above the point of 

 attachment of the basilar membrane to the spiral ligament appears a 

 prominent spiral ridge, the prominentia spiralis, the intervening groove 

 constituting the sulcus spiralis externus. The larger blood-vessel 

 (venous) within the prominence is the vas prominens. From the ex- 

 ternal sulcus there extend into the subjacent ligamentous tissue numer- 

 ous large clear clumps of epithelioid cells. These have been variously 

 interpreted as neuro-epithelial elements and as smooth muscle cells. 

 But Shambaugh (Archives of Otology, 37, 6, 1908) has shown that they 

 contain tubules which open into the sulcus, and that they are in reality 

 branched tubular glands. He ascribes to them the function of pro- 

 ducing at least a portion of the endolymph of the scala media; the stria 

 vascularis is probably also an important source of endolymph. 



The tympanic wall or floor of the scala media presents for examina- 

 tion several structures, which, from within outward (viz., from the 

 modiolus to the ligamentum spirale), are the limbus spiralis, membrana 

 tectoria, sulcus spiralis internus, basilar membrane, and the organ of 

 Corti which rests upon the basilar membrane (Fig. 587). 



The vestibular lip of the limbus spiralis presents a distinct eleva- 

 tion, which is formed by a peculiar cellular variety of connective tissue, 

 and is covered by columnar epithelium, whose cells are not sharply de- 

 nned from those of the underlying connective tissue. The surface of 

 the epithelium presents a distinct cuticular formation of considerable 

 thickness, which seems to be prolonged outward from the margin of 

 the vestibular lip, and forms the membrana tectoria. 



The surface of the limbus spiralis, when viewed from the scala 

 media, presents slight elevations which, at the margin of the vestibular 

 lip, are prolonged into prominent ridges whose indented borders over- 

 hang the sulcus and are known as the auditory teeth (of Huschke). 



The Membrana Tectoria (Membrane of Corti). This is an exo- 

 plasmic or cuticular tissue, formed by the epithelium of the inner or 



