35^ Journal of Comparative Neurology. 



other groups of fishes [than Dipnoi], I still adhere to the 

 hypothesis that the commissura interlobularis is a primitive 

 form of the whole transverse commissural system of the 

 hemispheres, thus representing both the anterior commissure 

 and the callosum." 



The facts above presented, while they seem to disprove 

 this position, serve to establish only the more firmly the 

 philosophical theory founded by Osborn,by which the struc- 

 tures above referred to are homologized throughout the 

 vertebrata. 



The so-called anterior commissure consists of three parts, 

 viz., a true commissural band connecting the two sides of the 

 base of the cerebrum; second, the decussation or commissura 

 of the radix mesalis olfactorii; third, the axial commissura, 

 first described by Edinger as the commissure of the basal 

 cerebral fasciculus. He says:(') " Diese commissur kommt 

 in alien Tierklassen vor, is aber bis jetzt nur einmal, von 

 Osborn gesehen worden, bei Reptilien. Mit der Commis- 

 sura anterior (com. interlobularis, autt.) darf sie nicht ver- 

 wechselt werden, sie liegt weiter hintern und gehort bereits 

 der Zwischenhirn an. Es ist mir fraglieh ob sie eine Com- 

 missur oder eine Kreuzung einzelner Biindel darstellt." The 

 commissure is of considerable size, and is closely associated 

 with the commissure of the radix mesalis. 



'Y^iG peduncles consist of three portions or bundles. 



The basal cerebral fasciculus, the decussation of which is 

 above noticed, Avas seen in ganoids and described as forming 

 a part of the anterior commissure. (■) In the drum it is en- 

 tirely distinct from the lateral motor and sensory tracts (only 

 the latter was included in the description just referred to). 

 This decussation lies between the praecominissura and the 

 decussation of the radix mesalis, and, after crossing, the fibres 

 may be traced some distance into the thalamus, passing on 



1 Edinger, Dr. L., " Untersuchung. u. d. vergl. Anat. des Gehirns," I ; " Das 

 Vorderhirn," 1888. 



2 Herrick, C. L., Journal of Comparative Neurologv, Vol. 1, p. 169. 



