





1. Tlio central i oped out of the thickened 

 11 of the outer germ- layer which is designated as the medullary 



plate. 



2. The medullary plate i to form t he i; 

 tube (medullary riilges, medullary groove). 



3. The formation >t' the neural tube exhibits three j.rin 

 modilication- : (//) Amp!.ixus. (J) 1 ' ) the re- 

 inaiiiiii.LT Yertel ral 



1. The lateral walls .t' the medullary tube become thickened, 



wlu-ivas t he do:>al and \ ent ral \\alU remain thin; li come 



to occupy the depths of the anterior and posterior iinal 



Basons, and constitute the commissures of the lateral halves of 

 the spinal cord. 



5. The- sj.inal cojdat first li 11s the whole length vertebral 

 1. lut ii g >-.\vlyt haii t h<- l:ittor,and finally terminates 



at tlu sccmul lumbar vertebra (explanation of the oblique course of 

 the lumbar and sacral nerves). 



6. The part of the ne-mal tuU which furms the brain becomes 

 segmented into the three- primary cerebral fore- 

 brain vesicle, mid-brain ve>irk, hind i 



7. The later*] walls of the fore-l.rain ve>ielo are evaginated to 

 i the optic vesicles, the anterior wall to form i -i.-s of the 



rum. 



s. The hind-brain vesicle is divided bye M into the vesicles 



of the cerebellum and ih_- medulla. 



9. Thus from the three primary bra in -vesicles there finally ; 

 live siv:mdary ones arranu'e 1 in a single series one after the ol 



(a) cerebral v->ii'l- (that of the hemispheres), (b) between-brain 

 le with the laterally attached los, (c) mid-brain 



vesicle, (d) vesicle of the cerebellum, (c) vesicle of the medulla 

 oblong 



10. The originally straight UOfl QD M to one 

 another later becomes at certain pla.--i sirirply bent, iu consequence 

 of which the mutual relations cf the vesii-les ai'e changed (cep: 

 ll-.-xure, poiital llexure, nuchal ilex 8 cephalic Or par; 

 protuberance at t he surface of the em responds to the cephalic. 

 lii-xure. the nuchal protuberanco to th^ nuchal flexu 



