39 6 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 



primary vesicle, the neural tube remains small and of nearly 

 uniform size; that part forms the spinal cord, in which the general 

 plan of development may be observed in its simplest form. 



IV. 



Fig. 114. Sections showing stages in the conversion of the medullary groove into 

 the neural canal. From the tail end of an embryo of the cat. (Gordinier after 

 E. A. Schafer.) 



ep,me,hy. Epiblast, mesoblast, and hypoblast. nt.g. Medullary groove, n.c. (in IV). 

 Neural canal, ch. Notochord. cae. Celom. am. Tail-fold of the amnion. 







In the very early stages of development two varieties of cells 

 make up the neural tube (Fig. 115). Certain very long cells, 

 during the karyokinetic growth, arrange themselves at right angles 



