79 
-chondrified and the neural arch itself has been incorporated 
into the skull. In ontogeny it appears as the occipital arch, 
some distance behind the auditory capsule and afterwards 
fusing witn it. leaving the foramen vagi between itself and 
the capsule (cf. fig. 21). It is SEWERTZOFF (1895, p. 262) 
who has compared the occipital arch with the first free 
vertebral arch in Petromyzon. 
It ís not easy to determine, from the somewhat diverg- 
ing statements of different authors, the number of seg- 
„ments incorporated into the skull by ths process and 
situated between the auditory capsule and the occipital 
arch. At any rate the glossopharyngeus and the vagus 
have been incorporated. However, the “spinalartiger Vagus- 
anhang”, the first spinal nerve behind the primary vagus, 
which, according to HATSCHEK, has fused with it in Gnathos- 
tomes, represents a segment also. In Necturus Miss PLATT 
(1897, p. 448. indeed found the vagus- Anlage to have a doub'e 
nature and to correspond to two somites, the second and 
the third post-otic ones. The anterior part of the rudiment 
of the ganglion extends outwards over the second somite, 
in the manner typical for cranial nerves, while the posterior 
‘part passes directly downwards, median to the third somite, 
in the manner of a typical spinal nerve, and becomes 
attached to the brain by the second vagus root. In Gymno- 
phiones MARCUS (1910, p. 378) finds close to the vagus 
ganglion another little ganglion, sometimes fused with the 
former and otherwise connected with it by fibrous nerve- 
strands, and which according to MARCUS (1. c.p. 451) must 
be homologized to the spinal ganglia and at the same 
time be counted to the vagus complex. To this little dorsal 
ganglion again a ventral occipital nerve, designated after 
FüRBRINGER's nomenclature (and thus wrongly) as z, shows 
close relations. The latter innervates the first myotome of 
the musculus dorsalis which is attached to the auditory 
capsule, in the same way as the third post-otic myotome 
in Petromyzon (cf. tig. 29) to which it evidently corres- 
ponds The next myotome is supplied by the first spinal 
nerve which has no dorsal ganglion. 
As to the number of somites to be observed in early 
ontogeny between the occipital arch and the auditory capsule 
in the head of the Amphibian, the statements of different authors 
do not wholly agree, but from recent inves igations it becomes 
more and more evident that in Urodelans, as in Pefro- 
