No. I.] THE VERTEBRATE EAR. ^7^ 



PI. VIII, Fig. 6; and PL XII). This plate, one part of which 

 has received the name of Hensen's Randkorper, another part of 

 which is known as the membrana reticularis, and whose third 

 and inner part has never been specially named, will be con- 

 sidered more in detail further on. 



The membrana basilaris is that part of the connective tissue 

 wall of the cochlear tube which lies under the sense organ and 

 forms its floor, as well as the basement membrane of its epi- 

 thelium. Like the basement membrane of all sense organs of 

 this system, it is a portion of the dermis of the head, modified 

 in the direction of homogeneity of composition. Its structure 

 and arrangement have been many times correctly described in 

 detail, and I have little to add to its histology ; but when we 

 consider its morphological significance, I am sure that hereto- 

 fore the true nature and relations of this now well-known plate 

 have not been correctly apprehended. It is far from being the 

 most delicate membrane of the cochlear wall, and is, as stated, 

 actually the thickest part of the connective tissue wall which 

 is exposed to the perilymphatic spaces. Reissner's membrane, 

 or the roof of the canal, is very much thinner and less resistant, 

 since its basement membrane is a very delicate plate and the 

 two plates of epithelial cells covering it are many times more 

 delicate than those supported by the cochlear floor. The mem- 

 brana basilaris has only one character that renders it of special 

 interest, and that is its relation as basement membrane to the 

 sensory cells whose nerves must pierce it in order to reach their 

 terminations. 



Boettcher thought he had proved a structural continuity of the 

 epithelium, i.e. the rods, with the basilar membrane, but from 

 his embryological studies he concluded that the layers of the 

 membrana basilaris were in no sense derived from the epithelial 

 layer supported on its inner surface. This conclusion no one 

 can refuse to acquiesce in when the evidence of comparative 

 anatomy is considered. The epithelial cells of the sense organs 

 of the lateral line are supported by the dermis on which they 

 rest, which thus constitutes the basilar membranes of these 

 organs. It normally develops lymphatic channels below the 

 sense organs. Thus the dermis between the organ and the 

 lymph spaces becomes the functional basilar membrane of 

 the organ, and is very much thinner than the surrounding 



