188 
J. BEA11D. 
Umbieguugsstelle iii das Gehirnrohr uaheliegendeu Ab- 
schnittes des Ectoderma/’ 
As in Elasmobranclis the first traces of the cranial ganglia 
Anlagen in the Chick are found in embryos in which as yet 
no division of the mesoblast has taken place. Marshall’s 
statement of the time of first appearance, viz. the twenty- 
second hour, may be taken to be as nearly correct as one can 
determine. 
The neural tube is still quite widely open. 
Figs. 86, 87, and 67 are sections through the head region of 
three such embryos. In fig. 86 no trace of the ganglion 
Anlagen is to be seen, but the epiblast is much thickened, 
especially in the region of the future central nervous system 
and ganglionic Anlagen. 
In fig. 87 traces may be seen of the ganglionic Anlagen at 
g. a., and one sees that they occupy practically the same posi- 
tion in reference to the central nervous system as the spinal 
ganglion Anlagen. In figs. 82, 83, and 84 are figured three 
sections through different regions of the head of a Chick em- 
bryo with seven body-somites. In all these sections the origin 
of the ganglia is very easily distinguishable. In fig. 82, which 
is through the region of the fore-brain, the limits of the neural 
plate are already marked out, and outside this the ganglionic 
Anlagen of each side are visible as special differentiations of 
the epiblast of the re-entering angle between the neural canal 
and the external epiblast, and also of a portion of the lateral 
epiblast beyond this. One notices that here, as in the spinal 
cord, the separation of the ganglionic Anlagen will cut out a 
particular region of the inner epiblast, and will leave a struc- 
ture at Z. which is comparable to, and, indeed, identical with, 
the Zwischenstrang of His in the region of the spinal cord. 
Fig. 83 is in the region of the mid- brain, while fig. 84 is 
taken farther back from the hind-brain ; these two sections 
present exactly the same appearances, and in a more marked 
degree than fig. 82. Figs. 77 — 81 are taken through the hinder 
head region of a Chick embryo with nine body-somites or so- 
called protovertebrae. Here the development of the ganglia has 
