MORPHOLOGY OF THE FOREBRAIN 497 



Fimbria 



Commissura hippocampi 

 Pars dorso-lateralis (lobus pyriformis) 



Cortex lateralis 

 Cortex intermedius (neopallium) 

 Corpus callosum 

 Nucleus olfactorius anterior 

 Bulbus olfactorius 

 The relative proportions of these parts which are evaginated 

 to form the cerebral hemispheres will vary as we ascend the 

 phyletic series. 



The rhinencephalon as commonly defined crosses the natural 

 boundries set in both of the preceding tables and therefore it 

 cannot be included within them. Nevertheless it, like the term 

 ophthalmencephalon which I recently proposed, stands for a 

 concept which has a certain morphological and physiological 

 value and should be preserved in our nomenclature. I would 

 subdivide it as follows: 



1. Bulbus olfactorius, containing the termini of the fila olfac- 



toria, the glomeruli, mitral cells and granules. 



2. Nucleus olfactorius anterior, undifferentiated olfactory tis- 

 sue of the second order, usually closely associated with the 

 bulbus, the two often being both represented in the terminal 

 swelling commonly called the bulbus, and extending backward 

 a longer or shorter distance between the true bulbus and the 

 more specialized parts to be next enumerated. 



3. Pars medialis rhinencephali. The olfactory centers in the 

 pars ventro-medialis hemisphaerii (corpus precommissuralis, 

 tuberculum olfactorium, nucleus preopticus, etc.,) and the 

 olfactory part of the hypothalamus. 



4. Pars lateralis rhinencephali, includes in fishes the tractus 

 and nucleus olfactorius lateralis and gives rise to the mamma- 

 lian lobus pyriformis. 



5. Pars dorsalis rhinencephali. Includes the dorso-medial ol- 

 factory tract and its nucleus in fishes and gives rise to the 

 hippocampal formation of mammals. 



6. The habenular nuclei and tracts also should logically be in- 



cluded in the rhinencephalon. 



