285 
branchs (as suggested already by GEGENBAUR, 1887, p. 68, 
again) according to FüRBRINGER, however, do not corres- 
pond to the hypoglossus of Amniotes. The latter is repre- 
sented by the ventral roots of the anterior free spinal nerves 
of Elasmobranchs. Thus there has been in Elasmobranchs a 
primary, and in Amniotes a secondary incorporation of 
vertebrae and nerves into the skull, accompanied each time 
by a loss of the dorsal roots of these nerves. 
This conclusion is based mainly on FüRBRINGER's con- 
ception of the Amphibian skull. Here no ventral roots were 
found to leave the cranium behind the vagus, the anterior 
spinal nerves supply the musculature which corresponds 
to the hypobranchial muscles in Elasmobranchs, supplied 
by GEGENBAUR's ventral vagus roots, and to the tongue- 
musculature in Amniotes, innervated by the hypoglossus. 
Ontogeny gives evidence of only one skeletal element in 
the occipital region, represented by the “occipital arch” 
(STöHR, 1879, 1881, GAUPP, 1893, SEWERTZOFF, 1895, PLATT, 
1898, GOODRICH, 1911). This is situated, in the same way as 
the neural archs of the trunk, in the myocomma between two 
myotomes, a little distance behind the auditory capsule 
(fig. 21 ), and is compared by SEWERTZOFF (1895, p. 260, 
262) to the first free neural arch of Petromyzon and to the 
anterior one of four similar vertebral rudiments described 
by HOFFMANN (1894) in the occipital region of Acanthias. 
The conclusion then seems obvious, and has been drawn 
by SEWERTZOFF, that the posterior occipital segments 
of Elasmobranchs and Amniotes and the hypoglossus roots 
supplying their myotomes have not yet been incorporated 
into the skull in Amphibians. 
This, however, is deemed improbable by FüRBRINGER 
(1897, p. 485), as the Amphibians would thus have a more 
Primitive position in this respect than Elasmobranchs (cf. 
also GEGENBAUR, 1887, p. 72). Though recognizing that 
ontogeny does not reveal any indication, however transitory, 
to support this view, he yet thinks it inevitable to assume 
that ventral occipital nerves, corresponding to the occipital 
nerves of Elasmobranchs, have once been present in Am- 
phibians but have aborted, and that the occipital region 
here too represents a multiplum of primary occipital ver- 
tebrae. Thus FüRBRINGER homologizes the cranium and 
especially the occipital region of Amphibians to that of 
Selachians, both representing a protometameric neocranium 
