The origin of tlie Corpus Callosum, a contrib. upon the Cerebral Comiu. etc 227 



is also a chiasma of the inner peduncular tracts which extend for- 

 ward to the olfactory lobes. 



In my papers upon the brain of Am ph in ma (1883) and Me no- 

 pom a (1 884), I accepted Stieda's views regarding the anterior commis- 

 sure in part, but confused the lower bundle witli the crossing of the 

 inner peduncular tracts, which takes place just beneath it, as des- 

 cribed and figured by Bellonci. 



Rabl-Rückhard (1883 pag. 303) independently of Bellonci's 

 Memoir adopted Stieda's view of the homologies of the upper and 

 lower bundles. He observes as a difficulty in this comparison that 

 while the Pars temporalis of the higher vertebrates reaches the tem- 

 poral lobes, with doul)tful connections with the central lobe (corpora 

 striatal, in the Amphibia its fibres terminate in the central lobe thus 

 forming a commissure of the brain stem. 



Bellonci was the first to prepare and figure sections in the 

 plane of the upper bundle of Rana and present the new view that this 

 is rather a chiasma than a commissure and has a posterior connection 

 with the optic region, as in the case of his «olfactory chiasma« in 

 Anguilla. His mention of the inner olfactory tract is also new. 

 As regards the lower bundle this author agrees with Stieda and 

 Rabl-Rückhard. 



Reptiles. 



Stieda (1875 pag. 66) described in the brain of the Turtle, Emys 

 europaea, similar upper and lower bundles uniting in the lamina 

 terminalis. The lower bundle he found to disappear laterally in the 

 brain stem while the ui)per extended forwards into the inner mantle. 

 «Der untere quere Theil der Kommissur dürfte der sogenannten Com- 

 missura anterior . der obere dem Corpus Callosum im Gehirn der 

 Säugethiere zu vergleichen sein.« It is singular that this author did 

 not remark the similarity of this upper bundle with that in the Am- 

 phibia and compare the latter also with the corpus callosum. 



Rabl-Rückiiard (1878 pag. 364) described in the lamina termi- 

 nalis of the Alligator brain, an ui»})er bundle, but failing in material, 

 did not observe a lower bundle. The former from uncertainty as to 

 its real homology was named commissura palii anterior since 

 it supplied the inner walls of the hemispheres. Recognizing its iden- 

 tity with Stiedas upper bundle in the Turtle he diftered from this 

 author in regard to its homology, on the ground that it corresponds 



MorpUolog. Jahrbuoli. 12. 16 



