64 AYERS. [Vol. VI. 



dermis. These modifications do not affect the relation of the 

 epithelial cells to the connective tissue cells, and the two layers 

 retain their structural independence. 



The basilar membrane of the organ of Corti is a complex 

 structure composed of cells and fibres of varying sizes, which 

 have arisen from the dermis. These fibres run both directly 

 and obliquely across the open basilar space, and form a two to 

 several layered floor, on which the cochlear organ rests. Anat- 

 omists have made various divisions of its surface, based usually 

 on the relative position of the cochlear ridge and the nerve 

 foramina to the surface of the plate. It is usually divided first 

 into two main zones, an inner and an outer. The former is very 

 sparsely striated, i.e. fibrous ; for in this part the individuality 

 of the fibres is more or less in abeyance. This part bears the 

 organ of Corti, and runs under the sulcus spiralis internus, 

 where it is perforated by the foramina for the nerves, to its 

 insertion into the limbus spiralis. 



The outer zone is usually considered to begin in the imme- 

 diate neighborhood of the feet of the outer pillars of Corti, i.e. 

 outside the arch of Corti, and extends from this region out- 

 ward to its insertion in the angle of the ligamentum spiralis. 

 The fibres of this zone are very distinctly separated from each 

 other, and are easily separated in microscopic preparations of 

 the membrane. 



There are at least two layers of fibres present in this mem- 

 brane in all mammals, and in some three and four. There is a 

 general agreement among investigators that the basilar mem- 

 brane of the human ear is thinner and relatively broader than it 

 is in most, if not all, other mammalian species, a belief which I 

 think is insufficiently borne out by the facts, but the number 

 and completeness of the layers of fibres is subject to change 

 during development, and is different for different species. The 

 surface layers of both faces of the membrane are in the adult 

 usually incomplete, and appear as bundles or bands of fine fibrils 

 lying on the deeper layers of the membrane. 



The basilar membrane in the pig and ox shows during its 

 development that it is not in any way built up from the ecto- 

 epithelial structures lying on its upper surface and derived from 

 the surface of the head, nor from the meso-epithelial structures 

 evolved during the ontogenetic processes as cellular lining of 



