100 THE ANCESTRY OF VERTEBRATES 



in which a primary incorporation of vertebrae has taicen 

 place, "wenn ich auch den bisherigen ontogenetischen 

 Untersuchungen darilber iceine beweisende Kraft und na- 

 mentlich den gewiss recht complicirten phylogenetischen 

 Process zur Genuge aufhellendes Moment zuerkennen kann"' 

 (1. c. p. 485). 



Then, however, we cannot avoid assuming that the 

 hypoglossus of Amniotes does not correspond to that of 

 Elasmobranchs, the occipital nerves of the latter being 

 supposed to have already atrophied and disappeared in 

 Amphibians. The hypoglossus of Amniotes can only corres- 

 pond to the anterior free spinal nerves of Amphibians and 

 Selachians and thus the conclusion is inevitable that in 

 Amniotes an assimilation of vertebrae into the cranium 

 has occurred for the second time ("auximetameric neo- 

 cranium"). 



Objections to their views. — The views of FuRBRlNGER, 

 based on his admirable investigations, have found a 

 wide acceptance among zoologists. Yet, after having repeat- 

 edly studied his work and that of FRORlEP and others. 

 I am not convinced of the accuracy of the conclusions of 

 both these authors; on the contrary, my doubts have 

 increased each time so that now, after a careful study of 

 the results of embryological work on this subject, I feel sure 

 that both are wrong in several respects In the first place 

 I must object to the view of Froriep, that the hypoglossus 

 in Amniotes and Selachians has no connection with the 

 vagus and the accessorius, or, casuquo, the vago-acces- 

 sorius. If, with Gegenbaur, we consider the vagus and its 

 ganglion as a product of the fusion of four dorsal nerves 

 and their ganglia, then, truly, the discovery of more or less 

 vestigial ganglia to the hindmost roots of the hypoglossus 

 necessarily leads to the conclusion that the hypoglossus- 

 roots, after having lost their dorsal components and gai:glia, 

 secondarily have moved forward under the vago accessorius, 

 which in its turn has lost its ventral roots — however strange 

 such a displacement may look at first sight! If, however, with 

 several later investigators, we assume that the vagus has 

 arisen by the fusion of a lesser number of dorsal roots 

 or even was originally a single dorsal nerve (HATSCHEK, 

 1892, p. 157) which has "collected" the ventral parts of 

 the dorsal roots {rami post- and praetrematid) of a number 

 of nerves behind it ("partial polymerism" of the vagus), 



