Functional factors in the niorphology of the forebrain of fishes 173 



medial forebrain bundle. In Cyprinus (Sheldon) and Osmerus (Holm- 

 gren) there are long descending and ascending fibers which span the en- 

 tire distance, with which are associated numerous shorter tracts. From 

 the área olfactoria medialis ascending fibers penétrate the bulbus olfac- 

 torius, and this is the case aven in the carp where the bulbus is very far 

 separated from the telencephalon médium by an elongated crus. 



The fiber connections of the poorly developed área olfactoria latera- 

 lis of teleosts are imperfectly known. From the description of Holm- 



Fig- 25. — Amia calva. Schema of the centers of the telencephalon and dience- 

 phalon as seen in median section of the brain. Compare figures 6, 11 and 18. 

 The bulbus olfactorius is marked with broken horizontal lines, the dorsal and 

 ventral longitudinal zones with oblique lines, and the intermedíate zone with ver- 

 tical lines. The intermedíate zone is indicated as far forward as the área olfacto- 

 somatica, which is believed to have direct thalamic connections. Its most rostral 

 member, the área olfactoria lateralis, is not indicated. 



gren they are probably similar to those of the medial área. There are 

 also ascending fibers from the lateral área to the medial part of the área 

 olfactoria dorsalis and to the área olfacto-somatica. 



In addition to the medial forebrain bundle already mentioned, there 

 is a lateral forebrain bundle. These bundles in a general way are com- 

 parable with the corresponding fasciculi of Amphibia, but not exactly; 

 for, not only does the composition of these bundles differ in different 

 teleots, but both of them seem typically to have fibrous connections with 

 all parts of the área olfactoria. AU parts of the área dorsalis send des- 



