No. I.] THE VERTEBRATE EAR. c^-j 



regards the fibres passing out from the hair cells, or more 

 strictly the cylinder cells of the large epithelial ridge, as arti- 

 facts, but believes most decidedly that the rods on the tops of the 

 "hair cells" are genuine auditory hairs. He showed that the 

 membrana Cortii cannot have the relations which Boettcher 

 attributes to it, — is not so placed; that the third zone as a 

 continuation of the membrane of Corti does not exist, for, on 

 account of the migration of the pillar fibres, the pillars and the 

 lamina reticularis would be shoved under the striated portion 

 of the membrana tectoria. In the guinea-pig and rabbit he 

 found in the several spiral turns of cochleae treated with osmic 

 acid that the outer boundary of Corti's membrane was exactly 

 one-quarter of a cell breadth outside of the outermost hair cell. 

 The third zone of Boettcher's is equivalent to the (co-extensive 

 with the) fibrous network on the dorsal surface of the mem- 

 brana tectoria as described by Loewenberg. The fibres of this 

 zone cross the membrane fibres, and passing over onto the first 

 zone appear to end in a sharp border. 



This fibrous layer arises as Boettcher describes it, and always 

 lies thrown back. The bars {Balkeii) from which it arises is 

 the least elastic portion of Corti's membrane. As concerns his 

 earlier view, that the membrana Cortii filled the sulcus spiralis 

 during life, Hensen is unable to decide, and leaves the question 

 open. He is uncertain whether the embryonic cells separate 

 from the membrana Cortii with which they are so closely bound 

 at first, but he has never seen the membrane with body large 

 enough to fill the sulcus. Finally, Hensen describes a row of 

 knobs on the lower surface of the membrane. It is always pres- 

 ent in guinea-pig and rabbit, and is placed exactly above the 

 inner hair cells. 



Based on considerations of the anatomy and function of the 

 cochlea, Hensen considers it certain that the nerve fibres end 

 in the hair cells. 



Hensen discovered in the outer cells a peculiar structure in 

 the form of an oval capsule around which fibres were spirally 

 coiled — they reminded him of sense buds (tactile corpuscles). 

 Their normal position in the cell appeared to be directly under- 

 neath the cell cap. He found the capsules in other parts of 

 the cell, but concluded they belonged in the top, and had been 

 accidentally misplaced. As to their function, he favored the 



