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the roots of the hypoglossus nerve in Amniotes. Several 
authors have adhered to the view expressed by this double 
nomenclature (hypoglossus, ventral vagus roots) but aban- 
doned afterwards by GEGENBAUR (1887, p. 65) himself. 
FRORIEP’'s and FüRBRINGER's views. — Others, however, 
considered these nerves as ventral spinal nerves of which 
the dorsal roots have been lost, a possibility alluded to 
already by BALFOUR (1878, p. 205). This idea was worked 
out for the hypoglossus of Amniotes by FRORIEP (1882, p. 
296) who demonstrated the presence of rudimentary dorsal 
ganglia in the posterior roots of the hypoglossus in embryos. 
rom this, and also from the discovery of well-developed 
myotomes in the occipital region, he concluded that this 
region must have belonged tv the trunk, not to the primarily 
unsegmented head region (cf. p. 251) to which region FRORIEP 
also considers to belong the gill-slits and the vagus. According 
to him in Amniotes an assimilation of vertebrae into the 
cranium and a progressive backward extension of the 
latter, as first suggested by STÖHR (“der Schädel ist in 
stetem kaudalen Vorrücken begriffen”, 1881, p. 99), has occur- 
red, by which originally post-branchial (i.e. not-cerebral, 
but) spinal nerves were incorporated into the skull after 
having lost their dorsal roots and ganglia, of which however 
vestiges may be noted still in ontogeny especially above 
the posterior roots. 
The same idea has been applied again, some time after- 
wards, by FüRBRINGER (1897) — and before him already 
by others, as e.g. by GEGENBAUR (1887, p. 65) himself — to 
GEGENBAUR’s ventral vagus roots in Elasmobranchs, in which 
accordingly the skull has already assimilated a number of 
vertebre. The ventral vagus roots are considered as spinal 
nerves that only secondarily have shifted forward into 
the occipital region and under the vagus (vago-accessorius), 
at the same time being incorporated into the cranium. 
This view is based mainly on the circumstance that these 
ventral roots, though anastomosing with the vagus, yet on 
_the whole join the ventral spinal roots behind them, thus 
contributing to the formation of the cervico-brachial plexus, 
and further on the fact, that here too more or less vestigial 
dorsal roots to the posterior branches have been describe 
_ (VAN WYHE, 1886, p. 681, OSTROUMOFF, 1889, p. 364, 
DOHRN, 1890, p. 82). The ventral vagus roots or hypo- 
glossus (as formerly they were often designated) of Elasmo- 
