The origin of the Corpus Callosum, a contrib. upon the Cerebral Coram, etc. 225 



Commissura anterior besteht bei den Cyprinoiden aus einem größeren 

 dorsalen Abschnitt, (1) der eigentlichen Kommissur der Hemisphären 

 und einem von letzteren wohl getrennten, schwächeren venti-alen (2), 

 dem Ilomologon der Pars olfactoria der Commissura anterior der 

 Säuger.« 



Bellonci's observations (1882 pag. 557 and 1883 pag. 193), are 

 of great interest here, because he uses them to support his theory of 

 the Amphibian commissures which is quite opposed to that which 

 I offer. In An gu ill a he finds two olfactory tracts, the internal and 

 external. (1) The internal forms two bundles, one passing back into 

 the hemisphere of the same side, the other forming a chiasma with 

 the corresponding bundle of the opposite side. From this »olfactory 

 chiasma« the fibres pass into the region of the origin of the optic 

 nerve. (2) The external bundle also divides into two parts, one 

 disappearing in the hemisphere of the same side, the other forming 

 a true commissure which unites the olfactory bulbs (pars olfactoria ?) . 

 (3) Immediately below these bundles is the commissure proper of the 

 hemispheres, the commissura transversale. 



Rabl Rückhard (1883 pag. 301) criticizes the views of Fritsch 

 and Mayser, differing from both. In the Trout [Trutta], he describes 

 three bundles composing the cerebral commissures. (1) The most 

 dorsal of these passes upwards and forwards into the olfactory lobes 

 and is homologous with the Pars olfactoria of the anterior commis- 

 sure. (2) The large middle bundle spreads out horizontally into the 

 Central lobe ' where its fibres consisting of several groups intercalate 

 with those of the cerebral peduncles. This bundle is homologous 

 with the pars temporalis of the anterior commissure. (3) The lower 

 bundle also spreads laterally but cannot be followed far and cannot 

 be compared to any part of the anterior commissure. 



Ampliibia. 



Among the older authors Leuret and Blattmann both described 

 the corpus callosum in the Amphibian brain, but so indefinitely that 

 it is difficult to determine to what structure they referred. Reissner 

 however (1864 pag. 98) found the upper and lower bundles in the 



1 This Author has shown that the hemispheres of the Teleosts are not 

 homologous with the entire hemispheres of higher vertebrates but only with a 

 portion of the same, the stem (corpora striata), united with the olfactory- 

 lobes; the mantle being represented by the thin epithelial pallium. 



