635 



A PRELIMINARY COMMUNICATION UPON THE 

 CEREBRAL COMMISSURES OF THE MAMMALIA, 



AVITH 



SPECIAL REFERENCE TO THE MONOTREMATA AND 

 MARS UPI ALIA. 



By G. Elliot Smith, M.B., et Ch. M. (Syd.). 



(Demonstrator op Anatomy, University op Sydney). 



(Plate XLiv.) 



" The subject requires careful re-investigation, but if tiie currently received 

 statements are correct, the appearance of the ' corpus collosum ' in the 

 phicental mammals is the greatest and most sudden modification 

 exiiibited by the brain in the whole series of vertebrated animals — it 

 is the greatest leap anywhere made by Nature in iier brain work." — 

 Huxley, " Man's Place in Nature." 



The cerebral commissures of the non-placental mammal present 

 a simplicity of arrangement, which may be readily understood, so 

 that a study of their distribution is likely to throw a considerable 

 amount of light upon the more complicated systems of connecting 

 fibres in the brain of the placental mammal. The knowledge of 

 the arrangement of the commissures of the Pi'oto- and Metatherian 

 cerebrum, moreover, must have an important bearing upon the 

 proper understanding of the morphology of the brain of all sub- 

 mammalian Vertebrates, since the Monotremata and Marsupialia 

 form the connecting links between the latter and the higher 

 mammals. This tracing of the homologies with the Eutheria is 

 all the more important because the common descriptive terms 

 have mostly been originally applied to parts of the higher 

 mammalian brain, especially that of the Primates. 



During the present year, acting upon the suggestion of 

 Professor Wilson, to whom I am deeply indebted for much 



