532 "Journal of Comparative Neurology and Psychology. 



would pass through the optic chiasma and the interventricular 

 foramina. 'No other plane would cut hoth roof plate and floor plate 

 at the same level. Owing to the reduction of the ventral zone and 

 the enormous expansion of the dorsal zone of the telencephalon in 

 all vertebrates, only a small part of the sections of a series can cut 

 both zones, but a section in the plane mentioned may be taken as the 

 true or standard transverse section of the telencephalon. Figures 

 45 A, B, C, D show such sections of the fish, amphibian and human 

 brain. 



Summary and Conclusions. 



1. The neural plate is bounded bj neural folds which meet in 

 front at the terminal ridge. 



2. The optic vesicles are evaginated from the dorsal part of the 

 neural tube and are connected with one another by the 'primitive 

 optic groove. 



3. The optic chiasma is formed in the terminal ridge and there- 

 fore occupies the anterior border of the brain floor. 



4. The lamina terminalis is coextensive Avith the neuropore and 

 in most vertebrate embryos and many adults its upper border is indi- 

 cated by a recessus neuroporicus. This is always in front of the 

 interventricular foramina. At the lower border of the lamina is the 

 recessus prseopticus. 



5. The roof of the telencephalon is always a tela chorioidea. 



6. The formation of the optic ridge in anticipation of the optic 

 tract separates the hollow optic stalk from the primitive optic groove 

 and it becomes connected secondarily with the preoptic recess. 



7. The velum transversum is clearly present in mammalian 

 embryos as in all other classes of vertebrates. 



8. Just in front of the velum in mammalian embryos is a para- 

 physal arch. 



9. The plexus chorioideus of the lateral ventricles forms imme- 

 diately in front of the velum transversum and in mammals so 

 involves the latter that its identity is lost. 



10. The telencephalon is a complete segment or ring of the brain 

 as His believed. 



