6o 



EARLY EMBRYOLOGY OF THE CHICK 



sent fusions of more than one neuromere, the series of enlarge- 

 ments seen in the brain region of the chick may be regarded as 

 neuromeric. For convenience in designation the neuromeres 

 are numbered beginning at the anterior end. 



cut ectoderm. 



neural groove 



fih neural fold 



neuromeric 

 enlargement 



neuropore 



I ^v "1 neuromeric 



enlargement 



n ght neural fold 



prosencephalon 

 optic vesicle 



mesencephalon 



rhombencephalon < 



prosencephalon 



mesencephalon 



TTietencephalon 



myelencephalon 



C D 



Fig. 20. — Diagrams to show the neuromeric enlargements in the brain region 

 of the neural tube. (Based on figures by Hill.) 

 A , lateral view of neural plate from dissection of chick of 4 somites (24 hours) ; 

 B, dorsal view of brain dissected out of 7-somite (26 to 27-hour) embryo; C, 

 dorsal view of brain trom lo-somite (30-hour) embryo; D, dorsal view of brain 

 from 14-somite (36-hour) embryo. 



With the closure of the neural tube and the establishment of 

 the three piimary brain vesicles we can begin to trace the fate of 



