48 
we might rather expect that the backward extension of the 
series of gill-slits into the trunk region, which pushes the 
anterior nerves aside and thus favours the formation of the 
cervico-brachial plexus in Elasmobranchs, would pull the 
roots of these nerves somewhat in a backward direction. 
Would not then rather the old conception, defended by HIS 
(1887, p. 401, 414, 423) against FRORIEP, be the right one: that 
the three hy poglossus-roots of Amniotes, being indeed nothing 
else than the vent-al occipital nerves of Elasmobranchs, 
may be termed, like the latter, ventral vagus roots, not a, 
b, c but something like x, y, z which already in Elasmo- 
branchs contribute to the innervation of the hypobranchial 
musculature and to which they show such an undeniable 
resemblance in their situation, their peripheral distribution 
and in the reduction of their dorsal roots in rostro-caudal 
direction? “Die Trennung des Hypoglossusgebietes vom 
Accessorius- und Vagusgebiet”, says HIS (1887), “halte ich 
für eine durchaus künstliche und ich berufe mich in der 
Hinsicht auf die Beobachtung, wonach der Hypoglossuskern 
auf eine lange Strecke den motorischen Kernen von Acces- 
sorius, Vagus und selbst Glossopharyngeus parallel laufen”. 
(p. 401). “Ein einziger Blick auf die Disposition der Ur- 
sprungsherde genügt, um erkennen zu lassen, wie willkürlich 
es ist, das Hypoglossusgebiet vom Vagusgebiete trennen zu 
wollen und jenes dem Rumpfe, dieses dem Kopie zuzu- 
theilen” (p. 414). 
FRORIEP (1905, p. 120) himself does not join FÜRBRINGER 
in his deductions concerning the hypoglossus but feels 
inclined to homologize the occipital somites of Am- 
niotes to those of Selachians with which they agree In 
o many points. In this connection he still mentions the 
fact that the anterior end of the pronephros in Amniotes as 
well as in Selachians is found as a rule in the third somite 
behind the cranio-vertebral limit. Truly, too great weight 
should not be attached to this circumstance, since the 
situation of the first pronephric funnel is no more bound 
to a definite segment than that of the plexus of the limbs. 
Amphibian and Selachian skull. — As we have seen, the 
whole distinction of a proto-and an auximetamertic neo- 
cranium and of occipital and occipitĳo-spinal nerves, as far 
as concerns Amniotes, is based on FIRBRINGER's assumption 
that the skull of the Amphibians is equal in length to that 
of Elasmobranchs and that it is a protometameric neocrâ- 
