ORGANS OF THE BODY. 663 



spiral, memb. commences at the outer border of the organ of Corti, and 

 remains one might almost say happily free from further accessory 

 structures. Formed of the two periostea! laminae of the memb. basilaris 

 it presents a perfectly smooth under surface towards the scala tympani, 

 while the upper appears finely streaked as if fibrillated. The outer 

 border of the zona pectinate^ reaches the bony wall of the cochlea (fig. 

 606, i). Here opposite a low bony ridge (m), which Huschke has named 

 the lamina spiralis accessoria, it unites with the so-called ligamentum 

 spirals (I). The latter, a vascular mass, consists of an upper fibrillated 

 portion, and an under cellular part facing the scala tympani (Hensen). 



326. 



There still remain for our consideration the epithelial lining of the 

 canalis cochleae, and the mode of termination of its nerves. 



In the foetus this canal (fig. 606, C), is originally lined throughout 

 with epithelial cells (Koelliker). These present themselves as a single 

 layer of pavement elements, except in two localities, namely (1), at the 

 sulcus spiralis (d), and so-called habenula sulcata, and (2) in the position 

 of the organ of Corti (/). In the first of these positions the cell-layer is 

 stratified and overlaid with a membrane, the membrane of Corti (Cm). At 

 the spot indicated by (b), the epithelial mass forms a ridge which sup- 

 plies, according to Koelliker, material for the formation of the organ of 

 Corti, of the hair-cells, and as a cuticular structure of the lamina reticu- 

 laris also. 



If the membrane of Corti be closely examined in the full-grown 

 animal, it will be found to present (in the ox, for instance) a thickness 

 of 0'045 mm., and finely fibrous appearance. It commences upon the 

 habenula sulcata at about the same spot as that at which the membrane 

 of Reissner, already mentioned, arises. Its mode of termination exter- 

 nally is still a matter of controversy. According to Hensen, Gottstein, 

 and Waldeyer, it reaches to the organ of Corti, terminating very much 

 thinned in the neighbourhood of the external hair-cells. It rests immedi- 

 ately upon the lamina reticularis. 



The epithelium of the fully developed canalis cochleae consists, upon the 

 membrane of Reissner of a layer of large flat pavement cells. Smaller 

 and thicker cells are to be found on the outer parts of the canal and zona 

 pectinata, as far as the neighbourhood of the organ of Corti, where large 

 spheroidal, and at last perpendicularly elongated elements present them- 

 selves the "supporting" (Stiitzzellen) of Hensen, Under Cortfs mem- 

 brane, upon the habenula sulcata, it probably only occurs, on the other 

 hand, interruptedly, and in the sulcus spiralis Hensen only found a 

 single layer. 



The cochlea is supplied by numerous capillary networks situated in the 

 periosteum and lamina spiralis. Above the so-called ligamentum spirale, 

 especially, may be seen a peculiarly vascular streak, the stria vascularis 

 of Corti (fig. 606, o). Within the lamina spiralis the bony tissue and 

 nervous ramifications are traversed by a complex network, which com- 

 municates with a spiral vessel situated upon the under surface of the 

 plate, i.e., that facing the scala tympani. 



As regards lymphatic spaces, in the internal ear, we have only to 

 remark that injections from both subdural and subarachnoidal spaces 

 of the encephalon penetrate into the labyrinth (Key, Retzius). 



Turning now to the distribution of the corhlear nerve, the first point to 

 43 



