24 AVEJ?S. [Vol. VI. 



sturgeon is in all probability — indeed, I think there can be no 

 doubt about it — identical with the cord which I have described 

 above, and would consequently represent the saccular endolym- 

 phatic duct. Embryology will very likely reveal the whole truth. 



The first anatomist to record the structure of the so-called 

 oval {or round) window of the Elasmobranch ear was Scarpa, 

 who {250, 1789) described two round depressions which appear 

 on the top of the occipital region after removing the skin. The 

 floors of the shallow depressions are formed by thin connective 

 tissue membranes, which he likened to tympanic membranes. 

 Removing these, the membranous ear is exposed, or, as he 

 thought, the vestibular chamber alone.^ 



E. H. Weber (285, 1820) described with great exactness and 

 detail the Batoid ear (Raja niiraletiis, clavata, torpedo, and 

 aqiiila). 



He discovered two external openings (endolymphatic ducts) 

 for each ear of these animals. The anterior of these corre- 

 sponds to the endolymphatic duct of other authors, but accord- 

 ing to Weber, opens out on the surface, after enlarging into the 

 saccus endolymphaticus, through three tubes. These pores I 

 have figured on PI. I, Fig. 13, for Raja ocellata of the New 

 England coast. The pores of the aural canal also occasionally 

 communicate with the distal section of the endolymphatic duct. 

 In the Torpedo, however, Weber found only one canal leading 

 outward from the endolymphatic sac {loc. cit., PI. IX, Figs. 

 75-86). 



Recently G. B. Howes (144, 1891) has advanced the theory 

 that the thin membrane filling the fenestra vestibidi cartilaginei, 

 as described by Scarpa, is the first trace of the vertebrate 

 tympanum, and he calls attention to the presence of a mass of 

 " homogeneous semifluid stuff " which occupies the space be- 

 tween the skin and this so-called tympanic membrane. 



The homology which Howes seeks to establish cannot be main- 

 tained. The fenestras rotunda and ovalis of the mammalian ear 



1 In Scyllium, Cestracion, and Chimsera, where this region is covered deep under 

 muscles, these openings are small, and may be entirely absent. Among the skates 

 the openings are usually large and the membrane well developed. It is worthy of 

 note that in no case does the skin show any modification (as greater thinness) over 

 the foramen and its tympanoid cover as occurs over the true tympanum of other 

 vertebrates. 



