CHAPTER II 



THE NEURAL TUBE AND ITS DERIVATIVES 



Infolding of the Neural Tube. The vertebrate nervous system develops 

 from a thickened plate of ectoderm along the middorsal line of the embryo. 

 By the infolding of this neural plate there is formed the neural groove, which 

 becomes transformed into the neural tube (Fig. 6). The neural tube detaches 

 itself from the superficial ectoderm and gives rise through a thickening of its 

 walls to the brain and spinal cord. The latter is formed by a process of uniform 



Neural groove Neural plate 



Neural groove Neural plate 



Ectoderm Neural groove 



Neural tube 



Neural tube 



D 



Neural cavity 



Fig. 6. Development of the neural tube in human embryos (Prentiss-Arey): A, An early embryo 

 (Keibel) ; B, at 2 mm. (Graf Spec) ; C, at 2 mm. (Mall) ; D, at 2.7 mm. (Kollmann). 



thickening in the walls of the caudal portion of the tube. The derivatives of 

 the rostral part are well illustrated in the accompanying diagram (Fig. 7). 



Brain Vesicles. At an early stage in the development of any vertebrate 

 embryo the rostral portion of the neural tube is distinguished from the caudal 

 part by the more rapid development of the former, its walls bulging outward 

 to form three bulb-like swellings or vesicles, which together represent the brain, 

 and are named from before backward, the prosencephalon, mesencephalon, and 

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