Course of Sensory Stimuli 129 



E represents energy derived from tactile 

 impressions ; a n, the receiving or sensory tactile 

 organ from which energy passes to b.g., a ter- 

 minal tactile nucleus located in the basal 

 ganglia; a part of the instinctive working 

 energy attached to the living matter forming 

 the cells of this nucleus being set free, passes 

 to mn., a motor centre. At the same time some 

 of the energy set free by the nucleus b.g. ex- 

 tends to p., a tactile cortical or neopallial centre 

 setting free a part of its nervous energy which 

 extends to the motor cells mn. and infuses a 

 certain amount of nerve force into that derived 

 directly from the instinctive elements of the 

 basal ganglia, the result being manifest in the 

 skill or cunning of the muscular movements 

 made by the animal which are represented in 

 the diagram by the letters VA. 



The increase in the size of the cerebral cortex 

 in the ascending orders of mammals seems to 

 have outgrown that of the unyielding skull by 

 which it is enclosed, so that its surface layers 

 have become crumpled up so as to form a num- 

 ber of infoldings, or sulci, as they are termed ; 

 on the exterior of the hemispheres the sulci 



i 



