706 THE EAR 



limbus portion of the embryonic cochlear duct. It has a gelatinous 

 fibrillar structure, but lacks nuclei ; and, unlike the otherwise very simi- 

 lar otolithic membranes of the maculae and cristaB, it contains no calca- 

 reous products. Its free margin overhangs, or rests lightly upon, the hair 

 cells of Corti's organ. 



The tectorial membrane has been very carefully studied by Hardesty 

 (1908) in the pig, from whose cochlea he has been able to remove it entire. 

 It is said to measure about 30 mm. in length, to occupy the four turns of 

 the cochlea, to be about five times as wide and five times as thick in the 

 apical turn as at the basal end, and to have a section area in the apical 

 turn approximately twenty-one times and a volume ninety-five times the 

 area and volume of its basal end. It is described as consisting 'of a hyaline 

 matrix, probably keratin, in gelatinous form, in which are embedded the 

 very numerous fine fibers or threads of uniform size' (Anat. Rec., 8, 2, 

 1914). The membrane has a slight amount of elasticity, is of a semi-solid 

 character and possesses 'marked adhesiveness'; its specific gravity is said 

 to be but little greater than that of the endolymph. None of the fibers 

 extend the entire width of the membrane, none are attached at both ends, 

 and the greater number are attached at neither end (Hardesty, Amer. Jour. 

 Anat., 8, 2, 1908). Hardesty describes a stripe (Hensen's stripe) on the 

 under surface of the tectorial membrane opposite the row of inner hair 

 cells, which he explains 'as a line of intercrossing ends of fibers of the 

 under surface resulting from the process by which the growth of the mem- 

 brane terminates/ He describes also a thin, exceedingly delicate, 'acces- 

 sory tectorial membrane' along the under surface of the outer portion of 

 the chief membrane; only its outer edge is attached to the latter, and it is 

 bounded internally by Hensen's stripe, thus covering only the outer hair 

 cells. 



The Sulcus Spiralis Interims. This is a deep groove included be- 

 tween the vestibular lip of the limbus and the basilar membrane which 

 is attached to the tympanic lip. The sulcus is lined by flattened epi- 

 thelial cells, which are apparently continuous with those of the vestib- 

 ular lip, and like them are not readily distinguished from the under- 

 lying connective tissue. The epithelium is continued outward upon the 

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

 cells of which it is continuous. 



The Basilar Membrane (Membrana basilaris) . This is a thin but 

 resistant membranous structure, upon which rests the epithelium of 

 Corti's organ. Hardesty (1908) describes it as a 'flat tendon . . . whose 

 purpose is merely to strengthen the floor of the ductus cochlearis and 



