364 
From these three figures it appears that the limits of neural seg- 
ments on both surfaces are transverse grooves. The segments thus 
formed are nearly equal in size and can be distinctly counted, when 
examined closely by properly reflected light. Those in the anterior 
region are just as distinct as those farther back that develop into the 
segments of the medulla. The same morphological interpretation should 
be placed upon them all. 
Figs. 14, 15 and 16, represent different views upon the head end 
of an embryo 251/, hours old with 6 fully formed somites. It will 
be observed that segments are present in both dorsal and ventral 
regions and can be counted on the internal as well as on the external 
surface of the brain. The three anterior segments (1, 2, 3) constitute 
the fore-brain and embrace the optic evagination. Segments 4 and 
5 represent the mid-brain and 6 to 11 the hind-brain. 
Fig. 14. Fig. 15. Fig. 16. 
Fig. 14. Encephalon of a Chick embryo with 6 somites, 251/, hours old. Dorsal 
view. i, 2, 3 etc. neural segments; c anterior limit of mid-brain; e anterior limit of 
the hind-brain; g dividing line between segments 7 and 8 of the medulla, ‘X 50 dia- 
meters. 
Fig. 15. Right surface view of the same encephalon as represented in Fig. 14, 
Letters and figures the same. 
Fig. 16. Left half of the encephalon represented in Figs. 14 and 15. Internal 
surface exposed to view. 
