No. I.] THE VERTEBRATE EAR. yj 



Structures, such as shall be effective in mediating between the 

 nerve-end organ and the nerve. 



In concluding this paragraph I wish to propound the definite 

 thesis that there is an unbroken protoplasmic path from the 

 base of the hair cells to the brain cells, along which path the 

 auditory stimuli travel, and during which time and before leav- 

 mg the end cell they are transformed from mass motion to 

 molecular motion. 



After having traced the cochlear organ from the Fishes up to 

 the Saurians, and described its sudden and very remarkable 

 development in this group as exemplified in the Alligator, and 

 after having studied in some detail the main characters of the 

 higher mammalian ear, the determination of the characters of 

 the monotreme cochlea has become a truly enticing topic for 

 investigation. 



Urban Pritchard (216, 1881) has done the only work, of 

 which the results have been published, on the anatomy of the 

 membranous cochlea of the Monotremes, but his observations, 

 although valuable, are not so complete as we need at the pres- 

 ent time. The membranous cochlea is of course shorter (ap- 

 parent length) and smaller than the bony tube, but a very good 

 idea of its length may be had from the size of the latter. 



Pritchard gives one-fourth inch as the length of the bony coch- 

 lea in OrnithorhyncJms paradoxus (more accurately 6.3 mm.). 

 However, on account of its curvature around the end of the 

 lamina spiralis ossea, its entire length is greater than that of 

 the bony cochlea. It runs nearly horizontally forwards and 

 curves at the same time slightly outwards. The lagena ap- 

 pears as a swelling on the cochlear tube, much as in Saurians 

 (Alligator, Crocodile) and Birds. It has a greater diameter than 

 the rest of the cochlear tube, and is fliattened parallel with the 

 plane of the basilar membrane. The Sauropsid characters of 

 the Ornithorhynchus cochlea are then more prominent than the 

 mammalian so far as the general shape is concerned, but when 

 we come to the internal characters we find them so far as 

 known strictly mammalian. 



The Sauropsid organ has disappeared ; the mammalian organ 

 of Corti is well developed, but possesses two rows of inner hair 

 cells instead of the one usual among other types of mammals. 

 The neural cartilage of the Sauropsid ear has been converted 



