350 



HORACE W. STUNKARD 



"that an earlier segmentation is incorporated into this division 

 as follows: in the forebrain three primarj^ somites; in the mid- 

 brain two; and in the hindbrain, six or six and one half if the 

 portion of segment twelve that lies in front of the first somite is 

 added to the latter." 



Fig. 16 Frontal section through the right neural crest of an embryo of five 

 somites, showing same features as figure 15. 



Fig. 17 Sagittal section through the closing neural tube of an embryo of 

 ten somites, showing same features as figure 15. 



Fig. 18 Sagittal section of the floor of medullary tube of an embryo of five 

 somites, showing same features as figure 15. 



Fig. 19 Frontal section through the developing brain vesicles, showing the 

 later neuromeres. 



Fig. 20 Same section as figure 19, showing cell arrangement in the right wall 

 of the hind brain just anterior to the otic invagination. 



