51 
scured by FüRBRINGER's voluminous work of the latter year: 
“Nimmt man an, dass es eine Stammform gegeben hat, die 
in Bezug auf den Occipitalteil des Schädels sich wie die 
Amphibien verhielt, so würde sich weiterhin die Ent- 
wickelung in zwei getrennten Bahnen bei Fischen und Land- 
wirbeltieren bewegt haben”. Few, 1 think, will follow RABL 
(1888, p 656) in supposing that first in the Elasmobranch 
egg an accumulation of yolk has occurred which, however, 
in the Amphibian egg has been lost again for some 
unknown reason, has been reacquired in Sauropsids and lost 
for the second time in viviparous Mammals. Especially if 
we compare the early stages of development of Petromyzon, 
Elasmobranchs and Amphibia, it will be evident at once 
that in this respect also the Elasmobranchs represent a side- 
branch, however primitive they may be in other characters. 
In the structure of the brain also the Amphibia stand the 
nearer to Pefromyzon, a metencephalon having developed 
in neither of them, unlike Selachians and Amniotes. In the 
former two the hypophysis originates from the ectoderm in 
front of the mouth, in the latter two from the roof of the 
mouth-involution. Concerning the development of the cranial 
muscles also, EDGEWORTH (1911) finds that the Amphibians 
exhibit more primitive features than the Selachians. 
We could no doubt keep to the names proto- and auxi- 
metameric neocranium to express the difference in length 
of the Amphibian skull on the one hand and the skull of Am- 
niotes on the other. However, we should then be using these 
terms in aquite different sense from that attributed to them 
by FüRBRINGER, for in the protometameric neocranium have 
now been incorporated only the glossopharyngeus and the 
vagus and in the auximetameric neocranium only the nerves 
Y, 2, while the nerves a, b, c, the occipito-spinal nerves, at 
least in Amniotes, do not exist as such. Only if with FüR- 
BRINGER (1897, p. 362) we designate the last occipital 
nerve in Acanthias as a, have we probably to do so in 
Amniotes also, as will be shown at the end of this chapter. 
According to FÜüRBRINGER a protometameric neocrantum IS 
found e. g. in Scyllium. If, however, we use his terms in 
the sense mentioned above, Scyllium has an auximetameric 
Cranium. A somewhat different terminology will be propo- 
sed at the end of this chapter. 5 
Before combining the results of the above consider- 
ations into a general survey of the history of the head of 
