Functional factíjrs in the morphology of the forfbrain of fishcs 147 



As seen in cross section taken not far behind the olfactory bulbs 

 (figure 3), the área olfactoria is separable into three nuclei (medial, lateral, 

 and dorsal), each of which receives large numbers of fibers from the 

 bulbus olfactorÍLis. There is a fourth región termed by Johnston the 

 «striatum» which is here designated área olfacto- somática. Farther 

 spin.ihvard adjacent to the thalamus there is a fifth región, the área so- 

 mática. The characteristics and functio- 

 nal connections of these five regions will 

 next be suramarized. 



1. The área olfactoria niedialis ('nu- 

 cleus postolfactorius ventralis of Johns- 

 ton, 1898, 190I1 is directly continuous 

 behind with the nucleus preopticus inu- 

 cleus taeniae of Johnston, 1901, but not 

 of his later papers) and this in turn is con- 

 tinuous with the hypothalamus ifig. 2i. 

 The continuous longitudinal cellular co- 

 lumn formed by these three nuclei is con- 

 nected for its entire length by a tract 

 of descending and ascending fibers, the 

 medial forebrain bundle, or fasciculus 

 medialis telencephali itractus strio-thala- 

 micus ventralis, Johnston 1. This rela- 

 tionship prevails in the brains of all ver- 

 tebrates and is, therefore, probably of 

 fundamental significance. The hypotha- 

 lamus is believed to be a correlation cen- 

 ter for gustatory and various visceral 



and other systems. Non-olfactory fibers ascending through the medial 

 forebrain bundle from the hypothalamus for correlation with olfactory 

 fibers have apparently played an important role in the specific differen- 

 tiation of the nucleus preopticus and área medialis, both of which dis- 

 charge efferent fibers into the hypothalamus and the habenula. 



2. The área olfactoria dorsalis (termed by Johnston epistriatum in 

 1898 and 1901 and primordium hippocampi in 19111 is in contact witli 

 the bulbus olfactorius in front above the foramen interventriculare (fig. 2i. 

 It forms the dorsal part of the wall of the telencephalon médium for its 



Fig. 3. — Section through the te- 

 lencephalon médium of Acipcn- 

 ser. The plañe of section is indi- 

 cated by the line A-B ¡n the small 

 drawingbelow. Based on Johns- 

 ton (1898, fig. 2). 



