Johnston, Forchrain Vesicle in Veriehrates. 515 



transversiun marks this boundary dorsally is universally agreed. It 

 stands at some distance from the lamina terminalis, however, and 

 if the boundary line is to follow the latter it must run along the roof 

 of the brain and then around its front wall, an obvious absurdity. 



A recent writer on the development of the forebrain (Fanny 

 Fuchs, 1908) states that it is only for practical convenience in 

 describing early stages that the term telencephalon should be used at 

 all. Wliatever is left after the development of the hemispheres (she 

 recognizes tacitly that there is something left) should be reckoned 

 with the diencephalon. She states that in Rana the telencephalon 

 has no roof because the di- telencephalic groove meets the upper end 

 of the lamina terminalis. Since she has not studied early stages, 

 has not recognized the velum transversnm and gives no figures to 

 show what she includes in the lamina terminalis, her conclusions on 

 this point can have little value. Such figures as Friiulein Fuchs 

 gives show a long median ventricle extending far forward beyond the 

 interventricular foramina. The roof of this, as the writer's own 

 preparations show, is the same as the roof of the similar median 

 ventricle in all other vertebrates, namely a membrane reaching from 

 the velum transversnm to the upper border of the lamina terminalis. 

 Fraulein Fuchs has simply included this roof in what she calls 

 the lamina terminalis. This author has studied only the obvious 

 features in the later stages of the development of the forebrain and 

 these give no sufficient ground for any conclusions regarding the 

 morphological value of the telencephalon. There may be quoted here 

 the conclusion of His in his paper on the general morphology of 

 the brain (1892, p. 383) : "dass eine solche allgemeine Morphologic 

 nur dann endgiiltig zu gewinnen ist, wenn wir auf die allerersten 

 Entwicklungsstufen zuriickgreifen." 



The tela chorioidea of the third ventricle and lateral ventricles 

 requires some comment. It must be noted first that in all verte- 

 brates, embryo and adult, a membraneous tela extends over both 

 diencephalon and telencephalon from the habenular commissure to 

 the dorsal border of the lamina terminalis. In all vertebrates except 

 adults of higher forms there is an obvious narrow place in the nervous 

 brain wall between the diencephalon and telencephalon, and the tela 



