MORPHOLOGICAL STUDIES. 
189 
advanced a step farther. The boundaries of the central nervous 
system are well marked in all the sections, and one can see 
that the latter is not connected with the ganglionic Anlagen. 
In this series of figures, which go backwards to the hind-brain, 
the ganglia Aulagen are already separated from the epiblast 
outside the re-entering angle between brain and epiblast, but 
still connected with the epiblast of the re-entering angle. For 
Professor His’s satisfaction it may be added that in all the 
sections a Zwischenstrang is more or less developed. The next 
stages are shown in figs. 97, 46, 63, 65, 66, which are taken 
through embryos with, on the average, eight to ten mesoblast 
somites. The central nervous system with the ganglionic Aula- 
gen are now shut off from the outside by the meeting and 
fusion of the external epiblast. 
The lips of the neural tube itself have not yet closed, 
because the ganglionic Anlagan, which in some of the figures 
(figs. 97, 88, 46) have still a distinctly bilateral character, 
still exist between and above them. The ganglionic Anlagen 
soon become entirely separated from the epiblast, and in 
doing this leave behind them the traces of the limits of their 
epiblastic origin in the shape of a three-cornered ridge of 
cells which is identical with His’s “Zwischenstrang” 1 of the 
spinal region. It is figured at Z. in figs. 88 and 89. By the 
growth outwards from their position above and between the 
lips of the neural canal, the latter is able to close, and does so 
without having contributed a single cell to the formation of 
the ganglia. 
The ganglionic Anlagen now begin to grow downwards 
towards the lateral surface of the brain to the point at which 
they acquire their permanent and only roots of attachment. 
The attachment takes place as in Elasmobranchs, and what I 
said about these forms on this subject may be taken as holding 
for the Chick also. 
On the other hand, a portion of the “ Anlagen ” grows 
towards the lateral epiblast at about the level of the noto- 
1 There is no such structure in the head of the Chick or any other Verte- 
brate I have as yet examined as His’s Zwischenrinne. 
