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. 



anterior neuropore 



neuromeric 

 enlargement 



prosencephalon 



mesencephalon 



rhombcncephalon 



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 (so-hour) embryo; D, dorsal view of brain 

 from i4-somite (36-hour) embryo. 



\\ ith the closure of the neural tube and the establishment of 

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



