The origin of the Corpus callosum, a contrib. upon the cerebral comm. etc. 539 



ported by observations of Kabl-Rückhard (1883 p. 309) and Ful- 

 LiQUETS ' upon the homology between the amphibian and dipnoan 

 brain. This leads me to autici})ate that the corpus callosum will be 

 found in the Dipnoi. In regard to the other groups of fishes I still 

 adhere to the hypothesis that the commissurae inter lobular is 

 is a primitive form of the whole transverse ^ commissural system of 

 the hemispheres, thus representing both the anterior commissure and 

 corpus callosum. 



A doubt was expressed as to the presence of the pars olfactoria 

 of the anterior commissure in the Sauropsida. This has been re- 

 moved by the discovery of a complete anterior commissure, of the 

 mammalian type, in the ophidian brain. There was a question also 

 as to the homology of the posterior division caU of the corpus cal- 

 losum in Emys and Col urn ba. This is now shown to be the com- 

 missura cornu ammonis, a primitive division of the corpus callosum. 



The precise distribution of the anterior commissure has never 

 been satisfactorily determined hitherto. As it traverse the corpora 

 striata it is difficult to decide whether part of its fibres serve to con- 

 nect these bodies. The extensive material which I have examined 

 thus far gives considerable evidence that lös commissure passes 

 through the lower part of the corpora striata and is distributed to 

 different portions of the brain mantle. The only exception is in the 

 frogs brain where a part of the anterior commissure seems to supply 

 a mass of cells lying in the brain stem (fig. 1'). The disposition 

 of the cell and fibre areas bear upon this question. 



In the Amphibia the cells of the hemispheres are uniformly 

 massed around the lateral ventricles (fig. 10) and, in general, the 

 fibre tracts of the cerebral commissures lie external to the cell masses 

 and send their fibres inwards (figs. 11 and 12) This is true of the 

 corpus callosum although it lies in part next the lateral ventricle. 

 In the Sauropsida the cell areas are more scattered between the ventri- 

 cles and the cortex (figs. 16, 20, 23), the upper commissural tracts lie 

 next the ependyma cells of the ventricle and the fibres pass out- 

 wards (fig. 18). In the mammalia the principal cell areas are cor- 

 tical. In each case, with the exception noted above, the fibres of 

 the anterior commissure seem to extend to the cells of the mantle. 



' G. FuLLiQUETS, Recherches sur le cerveau du Protopterus annec- 

 tens. Dissertation, Geneve 1S86. 



- The fornix is thus excluded as it is not a transverse connuissure. 



Morpholog. Jahibucli. 12. 3(] 



