152 THE AUDITORY NERVE AND COCHLEA, BY W. WALDEYER. 



internally the epithelium of the sulcus spiralis internus, rest 

 against the internal pillars. The cells of the latter, from the 

 innermost part of the sulcus to the hair cells, become constantly 

 higher.* The hair cells themselves reach the crest of the arch, 

 so that this internal portion of the organ of Corti forms a slope 

 looking inwards from the arches. 



The reverse occurs with the external division, which is of 

 somewhat greater breadth, and in various species more or less 

 steeply roofs it in externally. It is composed of the three rows 

 of the external hair cells, and of the columnar epithelial cells 

 immediately adjoining them, the supporting cells of Hensen, 

 which become progressively shorter until they are continuous 

 with the simple cubic epithelium of the zona pectinata. 



Associated with this complex series of cells are still two 

 membranous cuticular formations, the membrana tectoria (figs. 

 321 and 322, M t\ and the lamina reticularis (fig. 331, I k; 

 fig. 326, D, surface view). 



The pillars of Corti, in profile views, have the form of a 

 slender Roman S (sign of integration). The upper enlarge- 

 ment is the " head " or " caput," the lower the " pes " or " foot," 

 and the intermediate rod-like connecting piece is the " body " 

 of the pillar. A peculiar appendage is attached to the head, 

 the " capitular lamina." The inner pillar has two of these, 

 which, however, are continuous with one another ; an internal 

 small one, which, when seen in profile, looks almost like a hook 

 (fig. 327, B g) ; but in surface views, and from without, appears 

 indistinctly as a dark crest (fig. 327, C D g) ; and an external 

 large one which, more or less curved, appears as a direct 

 laminar process of the body; this is arched like a hood over 

 the caput, and sometimes, as in Vesperugo (fig. 327, D), exhibits 

 a distinct excavation along the external surface. The caput of 

 the inner pillar projects outwards like a pyramid, with a some- 

 what blunt point (fig. 327, C D). The superior (vestibular) 

 margin is slightly prolonged, and at the lateral borders a shallow 

 excavation may also be observed. The basal surface of the in- 



* In no adult Mammal does the epithelium fill up this sulcus, though 

 this certainly appears to be the case in embryoes (Kolliker, Hensen), but 

 always for.ns a single layer as far as to the region of the internal hair cells. 



