DEVELOPMENT OF THE NERVOUS SYSTEM 



517 



Fig. 1 A medial sagittal section of an embryo of Stage IX. For relations see 

 figure 37. X 125. 



Fig. 2 A medial sagittal section of an embryo of Stage X. For relations see 

 figure 38. X 125. 



Fig. 3 A medial sagittal section of an embryo of Stage XI. X 125. 



Fig. 4 A medial sagittal section of an embryo of Stage XII. X 125. 



RP^FERENCES 



cp. (I., anterior evagination of epi- par. a., anterior paraphj'sial evagi- 



physis nation 



ep. p., posterior evagination of epi- j)nr. p.. posterior paraphysial evagi- 



physis nation 



ill. mes. /., di-mesencephalic fold /^ r., posterior commissure 



di. pi., diencephalic plexus /;./'. r/., post-velar arch 



ni. br., mid-brain .s. c, superior commissure 



par., paraphysis v. L, velum transversum 



posterior commissure, indicated by an area of ectoglea. Figure 2 

 gives the typical appearance of the epiphysial formation of this 

 age. It is composed of a well marked epiphysial arch , in the caudal 

 portion of which is the out-pocketing, mentioned in the previous 

 stage, which now contains a cavity. In the cephalic part of the 

 arch is a much less pronounced solid diverticulum and in this a 



