628 THE EAR 



slopes more abruptly. The greater portion of the spiral ligament, 

 therefore, is contained within the scala media. Here it is lined by 

 low columnar or cuboidal epithelium whose cells blend, without 

 dernarkation, 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 at- 

 tached surface of the epithelial layer. The middle of this area 

 presents a prominent vascular ridge, which is known as the stria 

 vascularis. 



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

 nation several structures, which, from within outward (viz., from 

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

 membrana tectoria, sulcus spiralis, basal membrane, and the organ 

 of Corti which rests upon the basal membrane (Fig. 457). 



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

 vation, which is formed by a peculiar cellular variety of connective 

 tissue, and is covered by columnar epithelium, whose cells are not 

 sharply defined from those of the underlying connective tissue. 

 The surface of the epithelium presents a distinct cuticular forma- 

 tion of considerable thickness, which seems to be prolonged out- 

 ward from the margin of the vestibular lip, and forms the mem- 

 brana tectoria. 



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

 media, presents slight elevations which, at the margin of the ves- 

 tibular lip, are prolonged into prominent ridges whose indented 

 borders overhang the sulcus and are known as the auditory teeth. 



The membrana tectoria (membrane of Corti) is apparently an 

 exoplasmic or cuticular tissue ; although it presents a somewhat 

 fibrillated appearance it contains no nuclei. Its free margin over- 

 hangs, or rests gently upon, the hair cells of Corti's organ. 



The sulcus spiralis is a deep groove included between the ves- 

 tibular lip of the limbus and the basal membrane which is attached 

 to the tympanic lip. The sulcus is lined by flattened epithelial 

 cells, which are apparently continuous with those of the vestibular 

 lip, and like them are not readily distinguished from the underlying 

 connective tissue. The epithelium is continued outward upon the 

 basal membrane to the margin of Corti's organ, with the innermost 

 cells of which, it is continuous. 



The basal membrane (membrana basilaris) is a thin but resist- 

 ant membranous structure, upon which rests the epithelium of 



