The origin of the Corpus callosimi, a contribution 

 upon the cerebral commissures of the Vertebrata. 



Part IL 



By 



Dr. Henry F. Osboru, 



Professor of comparative Anatom}', Princeton, '"U. S. A. 



With plate XXV and 5 figures. 



The materials and observations for this part of the present in- 

 vestigation v^ere chiefly collected in the Morphological Laboratory 

 of Cambridge University and I am much indebted to Mr. Adam 

 Sedgwick and his assistants for the generous facilities Extended to 

 me there. 



I received a series of Kangaroo pouch specimens ranging in 

 length from 3.5 to 7.5 centimeters. These supplemented the fine 

 series of sheep embryos which were supplied in Prof. Kupffer"s la- 

 boratory through the kindness of Mr. Alex. Boehm. These series 

 together gave a full history of the early development of the cere- 

 bral commissures in the mammalia. Mr. W. H. Caldwell placed 

 at my disposal two advanced Cera tod us embryos from his valu- 

 able Australian collection. With these I expected to determine 

 whether the corpus callosum is present in the Dipnoi, as I think 

 highly probable, but I found that although the fore and hind limbs 

 were well budded out, indicating an advanced age, the cerebral com- 

 missures were still undeveloped. The forebraiu of Ceratodus was 

 at this stage found to belong to the Amphibian type, with hollow 

 paired hemispheres and a large ventriculus communis. In other re- 

 spects the points left in doubt in the first part of this paper (Morph. 



