518 'Journal of Comparative Neurology and Psychology. 



no farther forward than the nucleus of the III nerve, or at most 

 the nucleus of origin of descending fibers in the medial longitudinal 

 fasciculus. The ventral commissural system is interrupted by the 

 downgrowth of the substantia reticularis to form the inferior lobes 

 and mammillary bodies. This downgrowth has so completely altered 

 the relations of parts in the diencephalon that it is practically impos- 

 sible to trace a boundary line between dorsal and ventral zones. The 

 inferior lobes themselves doubtless represent a part of the correlat- 

 ing substance of the dorsal zones (Johnston 1906, p. 277 and fol.). 

 7. Pallium of the Telencephalon. — A long discussion has been 

 waged over the subject of the general morphology of the pallium 

 since the discovery by Eabl-Riickhard (1882) of the forebrain roof 

 of teleosts. It would not be profitable to enter into the details of 

 this discussion. The hypothesis of Rabl-Rllckhard and Edinger 

 was to the effect that lower forms possessed no true or nervous 

 pallium, but that the membraneous pallium as seen in teleosts and 

 other fishes has been transformed into a massive pallium by the 

 development of nervous elements in it. The hypothesis of Ahlborn 

 was that the anlage or beginnings of the pallium of higher forms 

 must be found in the massive portions of the brain of lower forms, 

 that a membraneous (ependymal) roof can never be transformed into 

 a nervous pallium. For many years the Rabl-Riickhard-E dinger 

 hypothesis dominated the field of forebrain morphology by sheer 

 force of the authority of its sponsors. Studnicka made an effort 

 to show the truth of the Ahlborn thesis, but for the time was over- 

 borne by Edinger and his followers. Although in his first work the 

 present writer accepted Edinger's views, a wider study of the sub- 

 ject led him to a treatment in 1906 much more nearly in accord 

 with the view of Ahlborn and Studnicka. Kappers and others 

 have added to the discussion and with the fuller knowledge of the 

 comparative anatomical and embryological facts the general morph- 

 ology of the membraneous and nervous portions of the forebrain 

 may be regarded as a closed subject. Much of the discussion has 

 been due to misunderstanding and differences in the use of terms 

 and it will be sufficient here to define the terms applied to the parts 

 of the forebrain and indicate briefly the differences in form in various 

 classes of vertebrates. 



