THE THALAMUS 147 



sonal identity, and its distinctive disposition and 

 character. Animals at least as low in the scale as dogs 

 show very marked individual differences in these re- 

 spects, as everyone who has kept dogs knows very 

 well. There are also certain specific thalamic reflexes 

 and the discharge of thalamic activities upward into 

 the cerebral cortex. Finally, the thalamic functions 

 are under cortical control through an extensive sys- 

 tem of fibers from cortex to thalamus. 



These are probably some of the characteristics of 

 the thalamus in higher mammals, though of the de- 

 tails our exact knowledge is still meager. There are 

 few changes of radical import between the bram of 

 the frog and man in relative size of parts and ar- 

 rangement of the connections shown in Figure 29 

 except in the thalamus, cerebral hemispheres, and 

 parts dependent upon these. The apparatus of intern- 

 al regulation is fairly well organized in the. frog, and 

 the thalamus clearly plays a large part in these func- 

 tions; it is in the adjustments to outside events that 

 we see the greatest advance. For success in getting on 

 in the world depends largely on fitting our behavior 

 into the rapidly moving sequence of happenings 

 around us, whether in a frog or a man. The connec- 

 tion of the exteroceptive sense organs with the cere- 

 bral cortex and the development of the subcortical 

 apparatus subsidiary to these connections mark the 

 leading features of further advance in brain develop- 

 ment between frog and man. 



