660 MANUAL OF HISTOLOGY. 



of the spiral bony plate. Under the microscope it is seen to be made 

 up of simple, either homogeneous or streaked, connective-tissue, with 

 imbedded cells and scattered capillaries. For the rest, this eminence 

 decreases, both in height and breadth, as we ascend through the canal 

 of the cochlea. 



Upon the upper surface of this peculiar pectiniform structure (fig. 

 607, A) a number of not less remarkable longitudinal and bifurcating 

 ridges present themselves. These are the teeth of the first order of 

 Cortij or acoustic teeth of Huschke. 



In the first turn of the cochlea their length is 0*0451 mm., and diameter 

 0-0090-0-0113 mm. ; these dimensions fall, however, as we ascend. Inter- 

 nally, towards the modiolus, they become shorter and shorter, ceasing 

 suddenly; while externally they increase in length, overhanging with 

 their extremities the sulcus spiralis already mentioned. 



With this last structure the second division of the zona denticulata 

 commences, namely, the habenula denticulate, or externa, as it is called. 



It is again subdivided by Koelliker (and, indeed, unnecessarily so) into 

 two secondary divisions, an internal, which he calls the liabenula per- 

 forata (fig. 606, e) ; and an external (h), the liabenula tecta. The latter 

 is identical with the habenula arcuata of Deiters. 



The habenula perforata constitutes the floor of the sulcus spiralis, 

 that is, of its labium inferius, and increases in breadth as the summit of 

 the cochlea is approached throughout the turns of the canal, while the 

 habenula sulcata becomes narrower at the same time. 



It consists of simple connective substance, and is covered on its surface 

 facing the canal of the cochlea by closely set row of longitudinal emi- 

 nences, '0226-0 '01 128 mm. broad ; these are the apparent teeth of CortL 



Between the outer ends of these apparent teeth, which are completely 

 hidden by the teeth of the first order in the first, but only partially so in 

 the subsequent turns of the cochlea, small slits exist for the passage 

 of the cochlear nerves (fig. 608, h). 



Here, then, we have the boundary between the habenula perforata and 

 habenula tecta or arcuata. 



Its wall, or the membrana basilaris (fig. 608, a, b) (formed by a prolonga- 

 tion outwards of the habenula perforata and tympanal periosteum), sup- 

 ports upon its upper surface the organ of Corti, a structure of the most 

 remarkable kind, whose physiological significance is as yet by no means 

 understood (figs. 607, 608). This is also known as the papilla siriralis, 

 a name proposed by Huschke, and employed after him by Hensen. 



In this extraordinary organ may be distinguished two species of form 

 elements, namely, peculiar fibres and no less characteristic cells. 



The first of these, the fibres or pillars of Corti, consist of two rows of 

 band or pillar-like elements standing upon the surface of the membrana 

 basilaris, which is somewhat thinned here, and converging obliquely 

 above, where they meet with pointed extremities. Collectively they pre- 

 sent the appearance of a puffy elevation, holding a spiral course through 

 the coils of the cochlea. The whole being hollow, has not inaptly been 

 likened to a tunnel. 



Thus, in the organ of Corti, we have to distinguish between internal 

 (ft, m) and external (o) pillars. Both kinds of elements are not present, 

 however, in the same number. Two of the external pillars may usually 

 be counted to three of the internal (Claudius), 



