442 C. W. PRENTISS 



of it, have been described by some as ha\'ing a reticular struc- 

 ture. Held ('09) figures the membrana as arising from the ends 

 of the supporting cells of the basal epithelium in the form of 

 parallel fibers. Yet he does not show these fibers as continuous 

 with the cytoplasm of the cells, like the hairs of the auditory 

 cells, nor did he study horizontal sections through the membrana. 



To sum up the development of the membrana pre\dous to 

 fetuses of 15 cm., we may say that it is a cuticular organ with a 

 definite though irregularly chambered structure which is secreted 

 between, and at the ends of the cells composing the basal epithelium 

 of the cochlea. Both the greater and lesser epithelial thickenings 

 take part in its development, its outer zone arising between the cells 

 of the spiral organ. It appears first near the inner angle of the 

 cochlea over the labium vestibulare but growth in thickness here 

 soon ceases. Next it develops rapidly over the cells which later line 

 the spiral sulcus and form the inner supporting cells of the spiral 

 organ. Finally, in later stages {yet to be described), it grows rapidly 

 over the spiral organ. From a study of my preparations it ivas 

 not possible to demonstrate distinct fibers imbedded in a matrix 

 nor are there grounds for believing that hairs or cilia take part in 

 its developynent. 



18.5 cm. stage. The later stages in the development of the 

 cochlea show the further growth of the membrana over the spiral 

 organ, its attachment to the latter, and the metamorphosis of 

 the high columnar cells of the inner cell group to form the lining 

 of the spiral sulcus. We have seen in earlier stages that differ- 

 entiation of the cochlear duct is much more advanced in the 

 basal coil than in the apical. This difference is very marked 

 in a fetus of 18.5 cm. In figure 14 the microphotograph shows 

 sections of three turns on each side. The scalae are both large 

 in the basal turn but in the upper turns the scala tympani is 

 still small. The coagulated endolymph more or less completely 

 fills the scala vestibuli. It will be seen when compared with 

 the 13 cm. stage that the membrana has continued to grow 

 rapidly over the spiral organ in the two upper turns but its 

 growth has ceased and it has remained small in the basal turn. 

 Three stages in the development of the spiral sulcus and organ 



