MORPHOLOGY OF THE FOREBRAIN 435 



tions to corresponding parts of the homolateral cerebral hemi- 

 sphere. The development shows that these parts in both cases are 

 differentiated from the primitive central grey of the early embryo 

 by a more rapid cellular proliferation than occurs in the inter- 

 vening sulci; i.e., they are functionally defined. Accordingly, 

 we find them related by important fiber tracts which clearly 

 demonstrate the underlying functional motives of the differ- 

 entiation. 



The hypothalamus is continued forward directly into the pars 

 ventro-medialis hemisphaerii, the whole column being an olfacto- 

 visceral center, the rostral end of which is receptive and the caudal 

 end efferent. 



The pars ventralis thalami is continued forward directly into 

 the pars ventro-lateralis hemisphaerii, the whole column in both 

 the telencephalon and diencephalon being the primary pathway 

 of efferent discharge into the somatic motor centers. 



The pars dorsalis thalami is the receptive center for somatic 

 sensory (exteroceptive) impressions and is functionally related 

 with the lateral wall of the hemisphere, probably (on comparative 

 grounds) chiefly with its dorsal part. 



The epithalamus corresponds in position with the pars dorso- 

 medialis hemisphaerii (primordium hippocampi) ; but the morph- 

 ological problems involved here are not as simple and self-explan- 

 atory as in the other cases and can best be discussed on a later 

 page (p. 468, ff.). 



Other Urodela 



The brain of Desmognathus fusca, as described by Fish ('95) 

 is very similar to that of Amblystoma. The figures show that 

 both primordium hippocampi and nucleus medianus septi are 

 less highly developed and the membranous septum ependymale 

 is extensive. In these respects adult Desmognathus seems to be 

 intermediate between the 17 mm. and the 35 mm. Amblystoma 

 larvae. No medullated fibers were found in the cerebral hemi- 

 sphere except in the lateral forebrain tract. The three dience- 

 phalic sulci are present as I have described them in Amblystoma, 



