MORPHOLOGY OF THE FOREBRAIN 463 



they provide for a correlation of the efferent impulses from the 

 cortex hippocampi with the somatic motor correlation centers 

 and for discharge through the latter. 



From the preoptic nucleus at the level of fig. 69 the habenular 

 tract arises in two parts, as in Amphibia, the tractus olfacto- 

 habenularis medialis passing up internal to the basal forebrain 

 bundle and the tractus olfacto-habenularis lateralis, laterally of 

 this bundle. The rostral end of the pars dorsalis thalami has 

 appeared and the limits of the pars ventralis are marked by sulci, 

 as in the Amphibia. 



I present one more illustration from this series (fig. 70), taken 

 through the optic chiasma and rostral end of the massa intermedia, 

 to illustrate the subdivision of the diencephalon. A nucleus dor- 

 salis is differentiated as in lower mammals and it is separated 

 from the remainder of the pars dorsalis by a shallow sulcus. The 

 lateral part of the pars dorsalis is closely related with the corpus 

 geniculatum laterale, as in the frog, and the optic radiations for 

 the hemisphere go out in company with the tractus thalamo- 

 corticalis. 



Elliot Smith ('03 and '10) has given a critical review of the 

 older ideas regarding the morphology of the reptilian cerebral 

 cortex which it is unnecessary to summarize here. The precise 

 homologies of the reptilian cerebral cortex in general cannot yet 

 be stated, in the absence of sufficiently exact knowledge of the 

 fiber connections of the various areas. The connections of the 

 dorso-median cortex bordering the primordium hippocampi 

 show it to be clearly cortex hippocampi ; but how far laterally this 

 formation extends we are not now in a position to decide. The 

 nucleus sphaericus (of Adolf Meyer and Edinger, occipito-basal 

 lobe of C. L. Herrick, epistriatum of Edinger and Kappers) in 

 reptiles may now be compared, in a general way, at least, on the 

 basis of its fiber connections, with the pars dorso-lateralis of the 

 frog brain and the pyriform lobe and amygdala of the lower mam- 

 mals; and it is very probable that the neopallium arose immediately 

 dorsally of this center which is known to receive both olfactory 

 fibers and projection fibers from lower segments of the brain. See 

 the further discussion on p. 488. 



