The Development of the Cartilaginous Skull and 
of the Branchial and Hypoglossal Musculature 
in Necturus. 
By 
Julia B. Platt. 
With Plates XVI—XVIII. 
Introduction. 
It is now several years since KASTSCHENKO ('88) first called 
attention to the fact that many cells of the neural crest in the head 
of the Selachian embryo do not take part in the formation of the 
nervous system, but give rise to reticular mesoderm, or mesenchyma. 
It was, however, already known to those interested in the early 
development of the nervous system, that the anterior part of the 
neural crest is not represented in corresponding ganglia. In 1878 
MARSHALL showed that the neural crest extends forwards to the 
level of the optic outgrowth, consequently beyond the region in 
which the ciliary and trigeminal ganglia are found. v. W1JHE (82) 
also described the anterior division of the neural crest in the Se- 
lachii as extending from the anterior part of the hind-brain even 
beyond the optic vesicles, thus occupying the whole width of the 
mid-brain. v. WiJHE tells us that this anterior part of the neural 
crest gradually vanishes from before backwards, adding that he 
cannot say with certainty what becomes of it. 
KASTSCHENKO, however, definitely states that the cells thus lost 
from the neural crest neither degenerate, nor take part in the 
formation of nervous tissues, but add themselves directly to the 
mesenchyma, a tissue which, in the opinion of KASTSCHENKO, is 
