THE CEREBRAL HEMISPHERES 155 



position corresponds with Brodmann's postcentral 

 area, the somesthetic cortex of man. 



These observations and others to be mentioned 

 later suggest that in the marsupials the anatomical 

 and physiological localization of cortical projection 



SU\CU6 



Fig. 37. — The electrically excitable cortical areas of the opossum as 

 charted on the dorsal surface of the brain. After Gray and Turner (1924). 

 /, extension of the fingers; 2^ fiexion of the fingers; J, flexion of the elbow; 

 /, twitching on the back of the forearm; 5, contraction of orbicularis 

 muscle of the eye; (5, movements of the snout; 7, erection of the ear; <?, re- 

 traction of vibrissae; 9, movements of the tongue; t;, erection of vibrissae. 



centers as we see it in man and other higher mammals 

 has not been completely attained. 



Gray has demonstrated well-defined anatomical 

 differences between the cortical areas of his chart 

 (Fig. 36)5 and most of these areas resemble in struc- 

 ture and position particular areas^of human and other 

 brains sufficiently to justify their comparison. Yet 

 this cortex is everywhere much simpler than the 

 human, and the anatomical differences between the 

 several areas are less clearly marked. 



