No. I.] 



THE VERTEBRATE EAR. 



17 



The canals among the Elasmobranchs have retained more of 

 their primitive relations to the utriculo-sacculus than those of 

 any other group, except the Cyclostomes. This is due to the 

 fact of the greater separation of the canals by the presence of 

 the double-chambered utriculo-sacculus between them, which in 

 the higher forms becomes more and more indistinct and reduced 

 by the migration of the main portion of the sacculus ventrad 

 of the utriculus, its upper portion only being left in connection 

 with the utriculus. 



Hasse and Retzius both describe the ear of Myxine as pos- 

 sessing but one semicircular canal, which they term the vertical 

 canal, and Retzius further regards the single canal arch in Myx- 

 ine as the homologue and forerunner of the utriculus of the 

 Gnathostome vertebrates. Since the single tubular arch in Myx- 

 ine rises at either end out of an ampulla, just as the anterior and 

 posterior vertical canals of all other forms take their origin, and 

 since the ampullae of the two ends of 

 the canal in Myxine are related to 

 the utriculus as regards the anterior 

 ampulla and the sacculus as regards 

 the posterior ampulla in exactly the 

 same manner, both with respect to 

 the walls of the chambers and the 

 sense organs contained, as they are 

 in all forms above the Hagfish ; and 

 finally and especially since the an- 

 terior and posterior roots of the au- 

 ditory nerve innervate the anterior 

 and posterior ends of the canal re- 

 spectively, it is an unavoidable con- positions of the contained sense 

 elusion that either the so-called single ^''S^"^- '^' ""\f "'^ ^"^P^"^' ^^' 



posterior ampulla; c, anterior and 



vertical canal m Myxme is a product 



of the fusion of the two verticals of 



other forms, or that it represents a 



primitive undifferentiated condition. 



Especially so, since its near relative 



Petromyzon has two canals. These 



two canals, however, unite with each other before opening 



into the utriculo-sacculus, and it is only the common tube 



thus formed which lies between the point of union and the 



Cut 7. — The right internal ear 

 of the Hagfish {Myxine gluti- 

 nosa), seen from the inside or 

 cerebral face. Figure after G. 

 Retzius. The figure represents 

 the ear somewhat enlarged, and 

 does not show the shape or exact 



posterior canals; ca and cp, am- 

 pullar ends of the same; d, duc- 

 tus endolymphaticus; mu, macula 

 utriculi et sacculi; n, nerve branch- 

 lets; 11, utriculo-sacculus; s, sac- 

 culus endolymphaticus. 



