50 
Ontogeny teaches us that the occipital arch behaves 
at first exactly like a vertebral arch, originating in the 
myocomma between two of the post-otic myotomes and 
differing only from the neural archs following behind it in 
that it afterwards fuses with the auditory capsule, leaving 
the foramen vagi between the latter and itself. Much better 
founded, therefore, seems to me to be the view of STÖHR 
(1879, 1881) and SEWERTZOFF (1895, p. 252) that the 
occipital arch in Amphibians actually represents the neural 
arch of only one vertebra which according to SEWERTZOFF 
corresponds to the first free neural arch of Petromyzon. 
Truly, we must then assume with SEWERTZOFF (1897, p. 
410): “Bei Amphibien, wie ich hierbei hervorheben möchte, 
entspricht der ganze Occipitalabschnitt einem einzigen 
Segmenten, dem einfachen Occipitalbogen, so dass die 
Amphibien in dieser Hinsicht unter allen Cranioten, mit 
Ausnahme der Petromyzonten, die einfachsten Zustände 
zeigen”’ While the skull of Petfromyzon, as stated above, 
comprises, besides the prostomium, only two segments, 
the trigeminus- and the facialis-segment, this number eví- 
dently amounts to five in Amphibians, the meta-otic glos- 
sopharyngeus-segment and those of the primary vagus 
and of the “spinalartiger Vagusanhang’” having been 
added to the cranium. This conception of the Amphibian 
cranium is strongly supported by the recent researches of 
Miss PLATT (1897) on Necturus and of GOODRICH (1911) 
on Siredon. In Elasmobranchs and Amniotes some two or 
three, sometimes even a few more, segments have been 
incorporated into the occipital region. We shall revert 
to this at the end of the chapter. 
The halo of primitiveness which since GEGENBAUR, 
BALFOUR and VAN WYHE surrounds the head of the Elas- 
mobranch thus looses part of its glory. It, however, We 
call to mind that in no other group of Vertebrates do the 
structure of the egg and the early stages of development 
show so close an agreement with those of Cyclostomes 
as is the case in Amphibians, that especially in Urodelans 
the similarity is truly striking and that on the other hand 
the Elasmobranchs in these respects show a deviation from 
this simple type which nearly equals that found in Saurops- 
ids, we shall have less difficulty in accepting the view 
expressed by SEWERTZOFF (1897, p. 410) in two articles 
(1895, 1897) of which the influence has been greatly ob- 
