Functional factors ¡n tliu morj)h(jlogy of the foixbrain of fishes 149 



¡t discharges also into the epithalamus. It is much larger than the medial 

 arca, ¡t is histologically more highly differentiated, and its fibrous connec- 

 tions are more diversified, though these are as yet only imperfectly 

 known. Among others, there is a connection by correlation fibers from 

 the área olfacto-somatica of the opposite side of the brain through the 

 commissura anterior. These fibers arise (fig. 4) from laterally placed tan- 

 gential cells termed by Johnston «cortex». Fibers are described as 

 passing from the área dorsahs to the underlying área olfacto-somatica 

 and there is probably a similar connection in the reverse direction. 



The área dorsalis is a correlation center between strong olfactory 

 tracts from the olfactory bulb, fibers ascending from the hypothalamus, 

 and fibers from the underlying área olfacto-somatica of the same and the 

 opposite side. The efferent tracts enter the epithalamus and the hypo- 

 thalamus. It is the most highly differentiated correlation center of the 

 telencephalon and is regarded as the primordium from which is developed 

 the hippocampus of higher brains, and perhaps other cortical áreas. It 

 is termed by Johnston primordium hippocampi and by Holmgren pri- 

 mordium pallii. 



3. The área olfactoria lateralis (nucleus postolfactorius lateralis, 

 johnston, 1 898, IQOI) is not so clearly differentiated in Acipenser as are 

 the other two divisions of the área olfactoria. It occupies the lateral 

 surface between the bulbus olfactorius and the commissura anterior and 

 below the área dorsalis. It ¡s clearly represented in the nucleus olfac- 

 torius lateralis of higher brains. 



4. The área olfacto-somatica occupies the middle part of the massive 

 wall of the telencephalon médium between the three nuclei last described 

 (figures 3, 4). Its functional connections have been incompletely analyzed. 

 It is described as receiving no termináis of the tractus olfactorius, but it 

 is traversed by unmyelinated fibers of this system and it probably is a 

 part of the área olfactoria, as the corresponding región is known to be 

 in other lower vertebrates. Moreover it receives short fibers from the 

 overlying área dorsalis (fig. 4) which is an olfactory center. It is connec- 

 ted with the thalamus by ascending and descending fibers (fig. 4, tr.st. th.). 



This área was called corpus striatum by Johnston in 1 90 1, but in his 

 later reference to the subject (191 1 a, p. 5101 he is inclined to regard it 

 as really belonging to the área olfactoria, in part to the dorsal nucleus 

 and in part to the medial. His descriptions suggest to me that this is 



