The origin of the Corpus Callosum, a contrib. upon the Cerebral Coram, etc. 235 



be taken for part of the upper commissure of the hemispheres. We 

 may distinguish it however by its larger fibres and independent 

 course. It turns forwards and downwards, separating from the ad- 

 jacent bundle and descends in the direction of the olfactory centre. 

 It cannot be followed far enough to determine positively the fact of 

 its relation with the olfactory lobes. Such a relation seems to me pro- 

 bable on the ground that Fritsch, Bellonci and Kabl-Rlckhard 

 have each found a dorsal bundle connecting the olfactory lobes. 



The cerebral commissures in Cyprina carpio are more elaborate 

 than those hitherto described in the brains of other Teleosts. Mayser's 

 description is incomplete. It seems evident from a comparison of earlier 

 observations with my own, that the main commissure of the hemisphe- 

 res traverses the peduncular tracts ; I have found that it partly also 

 enters the hemispheres direct. We may compare the middle and 

 upper commissure of the hemispheres in Cyprina (cm" andern'"), 

 with Fritsch's middle commissure (2), in Scorpaena; with Bel- 

 lonci s lower commissure (3), in Anguilla; and Rabl-Rückhard's 

 middle commissure (2) in Trutta. To this should probably be 

 added the lower commissure observed by Fritsch , Rabl-Rückhard 

 and myself [cm'). It is clear that there is no fixed order followed 

 in the position of these commissures with reference to the olfactory 

 commissures, they are sometimes dorsal, sometimes ventral. This fact 

 alone is sufficient to invalidate the homology with the Pars temporalis 

 which Rabl-Rückhard has advanced for his middle commissure, 

 upon the ground of its position below the pars olfactoria. 



Similar evidence is found in the consideration of the olfactory 

 bundles that there is a high generic specialization in the brain of the 

 Teleosts. The internal and external olfactory tracts may be distin- 

 guished by the fact that the fibres of the former cross each other, 

 forming the so-called »olfactory chiasma«, while the latter form a 

 true commissure. The external olfactory tract [o.cm) in the 

 carp consists of a ventral and, possibly, of a dorsal bundle [cm""), 

 which we may compare with the upper bundle (I) described by 

 Rabl-Rückhard in Trutta and with Bellonci's external olfactory 

 tract (2), in Anguilla, which is also dorsal. The internal ol- 

 factory tract [ol.i) in Cyprina is identical with Bellonci's (1) and 

 Fritsch's (1), internal olfactory tracts, although in Anguilla and 

 Scorpaena they reach the median plane above the main commis- 

 sures of the hemispheres, instead of below as in the carp. 



Conclusions. In these comparisons some allowance must be 



