No. I.] THE VERTEBRATE EAR. 103 



birds and mammals. Our author concluded that the Platypus 

 possesses a genuine organ of Corti, with two rows of the pillars 

 of Corti ; but the organ is in general not so well developed 

 as in higher mammals, and greatly resembles the avian cochlea. 

 The lagena with its sense organ is still present. 



Nuel (1878, 206) accepts Boettcher's views, for the most part, 

 with reference to the structure of the membrane of Corti, but 

 does not agree with him in considering the hairs of the hair 

 cells artifacts. He considered the membrane to be soft and 

 non-elastic, and thought the polygonal depressions on its lower 

 surface were derived from the membrana reticulata. The inner 

 zone he found homogeneous, and is tunnelled by channels for 

 the reception of the apices of habenula perforata. The mem- 

 brana tectoria scarcely covers the membrana reticularis. Its 

 outer zone is covered by a system of relatively large (coarse) 

 anastomosing fibres. Nuel could not decide whether a consid- 

 erable space was included between the membrane of Corti and 

 the epithelium of the sulcus spiralis. 



Although agreeing in the main with Boettcher regarding the 

 structure of the membrane of Corti, Nuel adds a few new facts 

 which his studies enable him to give beyond the former's ac- 

 count. The membrane of Corti is thrown like a plate or wing 

 upon the habenula sulcata and the organ of Corti. It thus 

 covers the habenula sulcata, the sulcus spiralis, and the organ 

 of Corti in a radial direction. 



In the spiral direction it extends throughout the whole length 

 of the cochlear canal. It begins as a thin plate on the habenula 

 sulcata, not far from the line of insertion of the Reissner's mem- 

 brane, and in this region is composed of a homogeneous sub- 

 stance, and perforated by large holes which permit the passage 

 of the processes of the habenula perforata, which are conse- 

 quently not covered by the membrane. One might say that 

 the membrane of Corti commences as a system of anastomosing 

 trabeculae lodged in the grooves of the habenula perforata. 



At the extremity of the teeth of the first row, the membrane 

 thickens considerably and passes out over the open space of the 

 sulcus spiralis, from whence it passes on to the summit of 

 the arch of Corti, but is there appHed to the membrana reticu- 

 laris. 



At the apex of the organ of Corti it sustains a considerable 



