140 Irving Hardesty 



rations used here, a thin fibrous film may be discovered overlying the 

 entire surface of the greater thickening and inward upon what will 

 become the labium vestibulare. At the very beginning, the then very 

 short fibers stand vertical to the epithelium and are even then aggluti- 

 nated by a seemingly fluid-like stage of the transparent matrix. From 

 pigs of 3 cm. up to 15 cm. the more important changes taking place 

 in the floor of the cochlear canal are a marked increase in both the 

 thickness and the width of the greater epithelial thickening and the 

 appearance and differentiation of the lesser thickening. 



At the stage when the labium vestibulare is evident, the greater 

 thickening wholly occupies the area of the future spinal sulcus and 

 consists of a high, pseudostratified epithelium whose surface is level 

 with the upward pointing tip of the labium itself (Fig. 10). As to 

 be inferred from this condition, the continuation of the epithelium 

 upon the labium is very much lower than that of the thickening proper. 

 In fact, this portion comprises the inner, tapering edge of the thickening 

 at the stage before occurs the differentiation of the mesodermal tissue 

 into the limbus spirale and its labium vestibulare and when the whole 

 is covered by the delicate beginning of the tectorial membrane. The 

 epithelium upon the labium is thus thin from the first, remains so 

 throughout, and takes part in the production of only the thin, tapering, 

 permanently attached, inner zone of the tectorial membrane. In 

 realit}^, it ceases as an epithelium, and probably altogether, in the adult 

 cochlea, for then the only superficial cells of the labium are those which 

 are situated between and level with the horizontal connective tissue 

 bundles comprising the auditory (Huschke's) teeth (see Fig. 9). Prob- 

 ably it ceases quite early to produce tectorial membrane, for, from 

 pigs of 12 and 14 cm. upward, the inner, attached zone of the membrane 

 gains apparently very little in thickness. 



As the greater epithelial thickening increases in width during the 

 earlier stages of the development, the fibers of the tectorial membrane, 

 standing vertical to the epithelium at the very first, are gradually drawn 

 outward from the more firmly attached inner zone, so that, by the time 

 a membrane has gained a more appreciable thickness, 10 cm. pigs, the 

 first formed portions of the fibers come to lie horizontal or nearly 

 parallel to the surface of the epithelium while their continuations curve 

 downward till the growing ends of the fibers only are vertical to the 

 cells of the parent epithelium. In this way is produced the transverse 

 striations apparent in the upper surface of the adult membrane and 



