THE NEOPALLIUM. 



357 



logenetic and ontogenetic development of the several main regions 

 of the forebrain show that the neopallium began its history at the 

 front end of the forebrain and that it has expanded backward. 

 Consequently the centers which were first developed must now be 

 found in the posterior part of the hemisphere and those which 

 were last developed, in the anterior part. The visual centers, 

 then, which occupy the extreme occipital pole, were first formed, 

 next the auditory which are depressed into the temporal lobe by 

 the development of the association centers, and last the somaesthetic 

 and somatic motor area. It was pointed out in the last chapter 

 that a forerunner of the neopallium is probably present in the fish 

 brain in the form of a tract from the tectumopticum to the forebrain, 

 and this accords well with the conclusion that the visual center 

 was the first to be developed in the cortex. The order indicated 

 by the position of the organs in the cerebral cortex of man accords 

 also with the order of importance of the sense organs in phy- 

 logenetic history. While the cutaneous system is the oldest it is 

 also the least specialized. The eye is the first special somatic 

 sense organ in vertebrates and the auditory system followed it. 

 It may easily be seen that these special sense organs which give 

 knowledge of objects at a distance would be of greater value for 

 the development of a higher correlating center such as the cortex 

 than the cutaneous system. Although the cutaneous system 

 was the last to reach the cortex its center hi the neopallium has 

 become larger than both visual and auditory combined. The 

 relative areas are approximately proportional to the number of 

 peripheral sensory fibers. The great importance of the somaes- 

 thetic area in apes and man is connected with the development 

 and mobility of the limbs; especially with the high organization 

 of the hand as a grasping and tactile organ, and the use of tools. 

 It may be supposed that while the senso-motor areas were being 

 developed, association centers made their appearance between 

 them, and that the posterior association center is therefore older 

 than the anterior. The expansion of the association centers has 

 helped to determine the position of the several areas in man. 

 Indications of this are seen in the shifting of the visual area from 

 a position about half on the mesial surface and half on the lateral 



