446 C. W. PRENTISS 



grown rapidl}^ outward beneatli the membrana thus pushing the 

 ends of its chambers outward. The result is that in this region 

 the chambers come to He parallel to the surface of the labium 

 and give the membrana a lamellated appearance which is espe- 

 cially marked in the lower turns of the cochlea. The membrana 

 may be divided into zones at this stage: (1) A thin structureless 

 zone over the inner portion of the labium vestibulare; (2) A 

 thicker second zone of flattened horizontal chambers over the 

 outer portion of the labium vestibulare ; (3) A still thicker third 

 zone of chambers curving downward and outward unattached 

 over the spiral sulcus; (4) An outer zone, thickest in the upper 

 turns with chambers trending downward, outward then inward, 

 largely attached to the cells of the spiral organ and probably 

 normally wholly thus attached. 



The sections of the 18.5 cm. stage thus show that the mem- 

 brana tectoria has developed rapidly over the spiral organ espe- 

 cially in the upper turns of the cochlea; that the membrana is 

 attached to the cells of the spiral organ in the upper coils and 

 shows shrinkage and distortion in the lower; that the inner cells 

 of the greater epithelial thickening degenerate or persist as the 

 lining of the spiral sulcus while the outer cells of this group form 

 the inner supporting cells of the spiral organ. Finally there is 

 no evidence of an inward shifting of the spiral organ sufficient 

 to account for the position of the membrana at this stage assum- 

 ing (which we do not) that it is not developed from the spiral 

 organ and that there is a necessity for such a displacement. 



The development of the structures arising from the basal epi- 

 thelium of the cochlea is practically complete at 18.5 cm., but a 

 number of cochleae were studied from the full-term fetus. The 

 structure of the membrana at this stage has been figured by 

 Shambaugh ('07) and Hardesty ('08) both of whom found attach- 

 ments between the cells of the spiral organ and the membrana. 

 These attachments are regarded as normal by many investi- 

 gators, as due to coagulation and shrinkage by others. There is 

 shown in figure 10 one of the many cases which occurred in in}- 

 preparations showing attachment to the outer supporting cells. 



