p AVERS. [Vol. VI. 



and since such structures accompany in an entirely similar 

 manner the sense-organ canals in fishes, we discover in this new 

 evidence of the nature of the cochlear tube. 



As is well known, the cochlear ganglion arises in contact with 

 the cochlear tube, and no sharp line of demarcation is at first to 

 be seen between the sensory epithelium and the ganglionic tissue. 

 This condition does not last long ; for as the tube increases its 

 size it becomes sharply marked off from the ganglion and before 

 long separated from it, mainly, as it would seem, by the ingrowth 

 of the intracapsular connective tissue, which at this time is 

 beginning to assume its cartilaginous nature. The separation 

 increases with the growth of the parts, until finally in the adult 

 the sense organs in the cochlear tube are connected with the 

 cochlear ganglion by a very long, narrow band of nerve fibres, 

 as viewed in section transverse to the long axis of the canal. 



The nerves pierce the floor (basilar membrane) about the line 

 of contact of the small and large epithelial ridges. 



The organ of Corti is the final product of a long series of 

 developmental changes in the cochlear organ. The earliest con- 

 dition of the cochlear organ in the mammal, which in its devel- 

 opment very completely epitomizes the phylogenetic history, is 

 of course the simple pocket budded off from the sacculus, its 

 inner surface being lined with a columnar epithelium. To con- 

 fine our attention to the points of most interest to us, we will 

 pass over all the changes between this earliest condition and 

 the stage in which the floor of the cochlear tube, now well 

 grown out, has become thickened, the thickening being in the 

 form of a ridge (later ridges) running parallel to the long axis 

 of the tube. Kolliker, Middendorp, and Boettcher have de- 

 scribed these elevations and applied to the two most prominent 

 ones, which play the greatest part in the subsequent history 

 of the mammalian cochlea, the names small and large epithelial 

 ridges. The large epithelial ridge lies nearest the lamina spiralis 

 ossea, and consequently is nearest the nerve supply ; the small 

 epithelial ridge lies beyond it outside, and receives its nerve 

 supply only after the nerves have been given off to or passed 

 through the large epithelial ridge. 



Owing to their subsequent history, I shall call the large epi- 

 thelial ridge the Sauropsid cochlear organ and the small epithe- 

 lial ridcre the mammalian cochlear orgran or the organ of Corti. 



