98 THE BRAIN OF THE TIGER SALAMANDER 



the migration of the palHal gray from deep to superficial position and 

 its subsequent compHcations. A beginning has been made, and I have 

 at various times reported progress in this analysis and some discus- 

 sion of its meaning ('24c, chaps, xv, xvi; 'Md, p. 354; '26; '27, p. 315; 

 '33a; '336; '33e; '34a). Yet much remains to be done before we can 

 fill in those finer details of structure which the physiologist needs to 

 know in order to plan crucial experiments. Frogs are probably better 

 adapted for such experiments than are salamanders, and to this end a 

 more detailed analysis of the histological structure and connections 

 of the forebrain of the frog is urgently needed. Sufl5cient knowledge 

 of this structure is now available to enable the physiologist to explore 

 the instrumentation of some components of the behavior pattern, as 

 illustrated by a recent study by Aronson and Noble ('45). 



THE CORTEX 



More than thirty years ago I published some reflections under the 

 title given to this chapter ('13a). Though parts of that paper require 

 revision in the light of subsequent research, yet it sketches the back- 

 ground of the present discussion. Attention was called to Dewey's 

 ('93) concept of the organic circuit as a substitute for the classical 

 formulation of the reflex arc, as mentioned in the preceding chapter. 

 Some illustrations of these organic circuits were given in my article. 

 Here we need only to emphasize the fact that all behavior is the 

 resultant of their interplay, for which provision is made in the cere- 

 bral mechanisms, such as are described in this and other works de- 

 voted to neuroanatomy. These are all circular reactions between 

 receptor and effector organs or the related internal adjustors. In the 

 course of phylogeny, cerebral cortex has been differentiated as the 

 culminating member of a series of progressively more complicated 

 integrating mechanisms adapted to make more efficient use of the 

 preformed circuits of the brain stem in the interest of more flexible 

 behavior in terms of individually acquired experience, as contrasted 

 with the stereotyped patterns of the stem (for a convenient summary 

 of the human connections see Papez, '44). 



In this connection two sentences may be quoted from von Bonin 

 ('45, p. 52) : "It is of the essence of cortical organizations that sen- 

 sory and motor areas become divorced more and more from each 

 other — are pulled farther apart as it were — as evolution pro- 

 ceeds As we ascend the evolutionary scale, the cortex assumes 



