Functional factors in thc nK)rphology of the forebrain of fishes 155 



into the «striatum», and probably into the área medialis and the hypo- 

 thalamus ithe latter in the tractus paUii) '. 



Between the cellular column formed by the área olfactoria dorsalis 

 and epithalamus dorsally and that formed by the área olfactoria media- 

 lis, nucleus preopticus and hypothalamus ventrally there is a zone which 

 appears to be comparable with the área olfactoria lateralis, área olfacto- 

 somatica and área somática of Acipenser. In petromyzonts the área 



Fig. 9. — Transversa section through the brain of Ichthyomyzon at the level of the 

 foramen interventriculare, >: 36. From Herrick and Obenchain, 191 3. 



olfactoria lateralis has been evaginated and appears as the posterior lobe 

 of the cerebral hemisphere. It receives fibers from the bulbus oltacto- 

 rius and discharges into the epithalamus and hypothalamus. Below the 



* The suggestions made by Holmgren (1922) that the área dorsalis of this 

 description is diencephalic and comparable with the eminentia thalami of Amphi- 

 bia and that the posterior lobe of the cerebral hemisphere (área olfactoria lateralis 

 of this description) contains the primordia of the cerebral cortex of higher forms 

 are not admissible. The morphological relations of the parts favor the interpreta- 

 tion of Johnston here adopted, which is, in fact, definitely proved by the connec- 

 tions of the fiber tracts. 



