THE BRAIN AND THE BODY 199 



Mammal possibly had the physical advance placed 

 within its reach. The earliest eutherian Mammal 



FIG. 72 DIAGRAM TAKEN FROM THE DRAWING BY PROFESSOR 



G. ELLIOT SMITH OF THE BRAIN OF Ornithorhynchus. 



The brain is in medial section and the commissures are cut across. 



There is no corpus callosum. 



FIG. 73. DIAGRAM OF THE HUMAN BRAIN IN MEDIAL SECTION. 



The commissures are marked in a similar manner to those shown 



in Fig. 72. Note the size of the corpus callosum. 



possessed the cerebral condition which made it possible 

 for it to take full advantage of the physical advance. 



