The origin of the Corpus Callosum, a contrib. upon the Cerebral Comm. etc. 247 



small. It divides and is distributed as in the Reptiles but the divi- 

 sion representing- the corpus callosum is much smaller than that 

 representing the fornix. The anterior commissure consists princi- 

 pally of the pars temporalis, the pars olfactoria being reduced 

 or wanting. The corpus callosum is larger than the anterior com- 

 missure in the Amphibia and Chelonia but in birds it is much smaller. 

 These proportions are in relation to the thickness of the inner mantle. 

 In the birds accordingly, vrhere the inner mantle has suffered the 

 greatest reduction, the corpus callosum is a mere rudiment. In the 

 other groups described it is far from rudimentary. In comparison 

 with what we observe even in the lowest mammals, the size of the 

 cerebral commissures is diminutive in proportion to that of the hemi- 

 spheres (cf. figs. 1 and 2 al). With the distribution, text area in view, 

 we may find the explanation of the unexpected fact that the corpus 

 callosum is relatively smaller in the higher orders of reptiles and 

 birds than it is in the Amphibia and thus remove the difficulty sug- 

 gested by MiHALKOVics, that we should not expect to find the corpus 

 callosum in the reptiles when it is wanting in the more highly or- 

 ganised birds 1. 



In closing this article I take pleasure in expressing my appre- 

 ciation of the many facilities generously afforded to me in -Professor 

 Kupffer's laboratory in Munich where the greater part of this research 

 was carried on. My especial thanks are due to Mr. Alexander 

 BoEHM, the assistant in charge, for his friendly aid. 



It is interesting also to recall here a letter sent me in 1880 by 

 Professor Huxley, my friend and former teacher. Upon hearing that 

 I was about to study the Amphibian brain, he wrote, »be on the 

 lookout for the corpus callosum«, or in similar words. In course 

 of working out the problem of the cerebral comQiissures, this advice, 

 which had hardly been taken as serious at the time, was frequently 

 called to mind. 



1 No alterations in statement have been made in this article since it was 

 sent to the Editor, April lOtii, 1886. A second part is now in preparation 

 (July). H. F. 0. 



