The origin of the Corpus Callosura, a contrib. upon the Cerebral Comm. etc. 229 



die vordere Kommissur als einen weißen Faden sieht, so hat man 

 auch das Corpus callosum vor Augen, denn ganz dicht über ihr 

 (comm. ant.) bemerlit man einen zweiten sehr feinen Faden, der mit 

 ihr parallel geht . . . Geht das genannte Blättchen für sich nicht 

 weiter, sondern verliert sich am unteren und hinteren Kande der 

 strahligen Scheidewand, mit deren Fasern innig gemischt.« The 

 author gives his grounds which are very good for this homology and 

 accompanies the description by two excellent figures. He also des- 

 cribes accurately the anterior commissure. This observation was not 

 confirmed by subsequent authors. 



Stieda (1870) failed to find such a bundle in the brain of the 

 Duck, Goose or Sparrow and left the question of the presence of 

 the corpus callosum in the birds as doubtful. 



Mammals. 



The observations of Flower (1S65 pag. 6) and Sander (1868 pag. 

 716), upon the cerebral commissures in the Marsupialia and Monotremata 

 have an important bearing upon the ancestral origin of these struc- 

 tures, yet I find little or no reference to them in recent papers. 

 The brains of these lower mammals indicate what we are to look 

 for as the primitive condition of the corpus callosum and anterior 

 commissure. By comparing the highest marsupial (Macro pus) with 

 the lower marsupial (Didelphis) and then with the monotreme brain 

 (Echidna), we obtain reversed stages of development which enable 

 us to predict what the next lower stage will be found to be. 



Flower observes that the lesser proportions of the corpus callo- 

 sum, in the Marsupials, are compensated for in a remarkable manner 



Fig. 1. 



Sagittal and transverse sections of the Brain of EcUidna, 'Jj (after Flower), cal corpus callo- 

 sum. (icm anterior commissure, elf columna fornicis. cif Crura foraicis. spl Septum. 



by the immense size of the anterior commissure. The fibres of the 

 former bundle radiate over the whole of the inner wall, while those 



IG* 



