ORIGIN OF NEURON PATTERN 



197 



62 



Figs. 62-65. — Developmental stages of neural tube and spinal 

 ganglia in salamander, Amblysloma punctatum: Fig. 62, one side of 

 neural plate, showing early stage of neural fold; Fi^. 63, neural tube 

 just after closure, cells of neural crest indicated by shading; Fig. 64, 

 later stage, showing beginning migration of spinal ganglion cells; Fig. 65, 

 still later stage; cells of neural crest have migrated latcroventrally to 

 form spinal ganglion (from Johnston, 1906). 



