152 



Dr. U. Pritchard. 



[Dec. 9, 



Covering the limbus, crossing the sulcus, and covering the organ, is 

 a mucoid layer, the membrana tectoria. 



Nerve filaments pierce the upper lip of the sulcus and pass to the 

 hair cells and nuclear cells of the organ. 



The organ of Corti, with the membrana basilaris below and the 

 membrana tectoria above, form the lamina membranacea. 



The ductus cochleae commences as a delicate tube, no doubt con- 

 nected in some way with the saccule of the vestibule. Its termination 

 is very peculiar ; instead of ending with the lamina ossea, where the 

 organ of Corti ends, it is continued round the apex of the cochlea to form 

 three-fourths of a circle. Just past the end of the lamina it forms a 

 circular tube ; at the other side of the apex, it enlarges into an oval 

 chamber (lagena) which terminates at the base of the lamina ossea. 

 This lagena is lined by epithelium, chiefly cuboid, but with one large 

 patch of nerve epithelium, like the thorn cells and bristle cells found 

 in the maculae acusticae of the vestibule. (" Quar. Jour, of Micros. 

 Science," p. 379, 1876.) 



The cochlear branch of the auditory nerve passes through the bone 

 on a level with the floor of the tube, but to its outer side. It gives 

 off lateral branches all along to the lamina, and its terminal fibres go 

 to the lagena. The lateral branches pass through a ganglionic mass, 

 similar to the ganglion spirale, and then on through the lamina, close 

 to its lower surface, finally perforating the upper lip of the sulcus 

 by a single row of holes (habenula perforata) and entering the organ 

 of Corti as already described. 



Comparison of the Minute Structure of the Cochlea of the Duckbill with 

 that of Typical Mammals. 



From the foregoing description, the duckbill's cochlea is shown to 

 be so unmistakably mammalian in type, that merely the differences 

 will here be noted. 



The lamina spiralis membranacea increases in width, and so do its 

 component parts, from base to apex of the spiral cochlea ; in the 

 duckbill's this widening takes place, but not nearly to such an extent 

 as in the spiral cochlea. 



The rods of Corti in the duckbill are not so well developed as in the 

 typical mammal. 



The membrane of Reissner in this monotreme presents blood-vessels 

 on its surface with convoluted knots ; these I have never found nor 

 read of in this situation in any other mammal. The vas spirale of 

 the ordinary mammal is represented by two vessels in the duckbill. 



The course of the cochlear nerve necessarily differs in the two 

 forms of cochlea. 



But the great difference is found in the presence of the lagena at the 



