86 
general we see in Elasmobranchs rather a tendency of the 
skull to decrease than to increase in length, the highest 
number both of epibranchial and of post-branchial cephalic 
segments being found in the more primitive forms 
(Notidanids). FÜRBRINGER was also wrong in assuming that 
the skull in Amphibians is equal in length to that of 
Selachians and that here also the occipital ventral nerve, 
sometimes observed in early stages, must be termed z. Itis 
not z but x, the skull being shorter than that of Selachians. 
Head of Amniotes. — In sharks one (Scyllium, Pristiurus) 
or two (Acanthias) post-branchial somites belong to the 
region of the skull and a corresponding number of ventral occi- 
pital nerves are found to leave the latter and to participate at 
the innervation of the hypobranchial musculature. In Amniotes 
it is generally stated that the hypoglossus consists of three 
occipital (“occipito-spinal” after FüRBRINGER) ventral roots, 
that is one more than in Acanthias. Since in Amniotes the 
number of gill-slits is one less, we reach the conclusion that 
the backward extension of the Amniote skull corresponds 
to that of Acanthias and that, as in the latter form, the skull 
comprises eight segments. The number also of myotomes 
observed in the occipital region of Amniote embryos cor- 
responds on the whole to that found in Selachian embryos. 
e hypobranchial or tongue-musculature is formed again 
from the post-branchial myotomes, four in number, of which 
one does not belong to the skull. The tongue musculature, 
in fact, is supplied by a hypoglossus with three occipital 
roots uniting with the first free ventral root to a plexus 
which, however, in this case does not fuse with the plexuis 
brachialis which in Amniotes often shoves backwards 
pretty far from the head. 
Thus the Amniote skull represents a neocranium, corres- 
ponding in length to that of the Selachians. The intracranial 
(occipital) hypoglossus-roots may be designated with the 
same letters as those in Selachians, i.e. with the last, and 
not the first, letters of the alphabet. Only if, with FüR- 
BRINGER (1897, p. 362), we call the last occipital nerve of 
Acanthias a have we probably to do the same in Amniotes. 
The “ganglion hypoglossi”’ discovered by FRORIEP (1882) 
in the sheep and known also as FRORIEP’s ganglion, being 
the dorsal ganglion of the last head segment, evidently 
corresponds to the dorsal ganglion found in the last segment 
of the head in Acanthias (cf. fig. 31, sp. 8). In both cases it IS 
