No. I.] THE VERTEBRATE EAR. 55 



few dwarfed remnants remain in tlie place of the once powerful 

 organ of the Sauropsid type. The histology of the organ has 

 already been given by Boettcher (31, 1869), Kolliker (166, 1861 ; 

 164, 1879), Retzius (237, 1884), and others, but only in a very 

 incomplete manner. I am able to make some few additions to 

 it, based on observations made on the organ in its mature state. 

 The long cylindrical cells occupy the whole depth of the organ 

 and fasten upon the developing membrana basilaris. They are 

 polygonal columns, more or less bent, depending upon their 

 position in the organ (PI. VI, Fig. i). Within, the protoplasm is 

 clear and is provided with a single oval nucleus, which lies at 

 different niveaux in different cells and in different parts of the 

 organ. The cells are never multinucleate, as has been asserted 

 by Boettcher (31, 1869), From the top of each cell there rises a 

 long, slender hair structure, which curves over toward the inner 

 edge of the organ over the region of the entrance of the coch- 

 lear nerve. This part of the floor of the cochlear canal is on a 

 level (at this time) with the top of the cells of the Sauropsid 

 organ, although the floor is here not near as thick as it is under 

 (and including) the Sauropsid organ. In consequence, the hairs 

 seem to fall over on to the surface of this plateau, the inner 

 portion of which later on is known as the Limbus spiralis in- 

 ternus. 



Owing also to the relation of this plateau, when the Sauropsid 

 organ has disappeared the open canal occupied by the organ is 

 left free, and over this the hairs of the organ of Corti project, 

 roofing over the canal, but only incompletely closing it in. 



The human cochlea may be taken as fairly representing mam- 

 malian conditions. It is not so much coiled as the cochlear tube 

 of some of the higher Mammalia, but it stands much nearer the 

 apex of the series than to the lowest members, as represented 

 by Echidna and Ornithorhynchus, which are but little above 

 the avian and saurian conditions. The human cochlear tube is 

 a flattened canal having in different parts of its course a varying 

 cross-section, from nearly circular and oval to distinctly triangu- 

 lar form. In the adult ear it possesses about three spiral turns, 

 and along its floor, extending from one end to the other, is a 

 linear series of sense organs so closely united together as to 

 have been described as a single band-like sensory apparatus by 

 all anatomists from its discoverer, Marchese Corti (185 i), down 



