366 
V+ Ve N 
Fig. 20. 
Between the ages 
of 22 hours and 33 
hours I have a very 
close series of em- 
bryos in which the 
continuity of the 
neural segments, in 
the region of the 
medulla, is clearly 
established in both 
divided and dissec- 
ted specimens. I 
have also observed 
the disappearance of 
the five anterior seg- 
ments during this 
period of growth. 
The first three, or 
those of the fore- 
brain, disappear 
first). In Fie? 15 
these segments (1, 
2,3) are more clearly 
marked in the ven- 
tral zone of the brain 
Fig. 19. Encephalon 
of a Chick embryo, 50 
hours old. Right profile 
view. e anterior limit of 
the hind-brain; 6—17 its 
segments. Segment 6 the 
cerebellum. c anterior 
limit of the mid-brain; 
r anterior limit of the 
thalamencephalon; s dor- 
sal groove dividing the 
thalamencephalon; V fifth 
cranial nerve; VJZ and 
VIII seventh and eighth 
cranial nerves. X 36 dia- 
meters. 
Fig. 20. Encephalon 
of a Chick embryo, 80 
hours old. Right surface 
view. ep. epiphysis. Other 
letters and figures the 
same asin Fig. 19. X 19 
diameters. 
