January 7, 19 10 J 



SCIENCE 



15 



fibers are added, passing from the external 

 geniculate body of the thalamus to the 

 hemispheres, and also acoustic fibers from 

 the inferior eoUiculus of the midbrain. 

 Though there is no true cerebral cortex 

 here, the tissue from which it is to arise in 

 reptiles can be definitely identified and 

 this tissue is in the frog clearly divided 

 into a medial part, serving primarily the 

 correlation of olfactory and visceral re- 

 flexes, and a lateral part, serving primarily 

 the correlation of olfactory and somatic 

 reflexes. The former gives rise in higher 

 animals to the hippocampus, the latter to 

 the pyriform lobe (uncus), while the rest 

 of the cortex, or neopallium, is in these 

 animals differentiated dorsally between 

 these two masses and serves chiefly for the 

 correlation of non-olfactory reactions. 



The two parts of the pallium which we 

 call archipallium and neopallium (i. e., 

 olfactory and non-olfactory cortex) are 

 not of different age, as the names imply. 

 They probably both arose at the same time 

 to serve the delicate discriminative reac- 

 tions of the muzzle reflexes. Their pre- 

 cursors are found in fishes and amphib- 

 ians, where their cells are mingled in an 

 undifferentiated tissue which has been 

 called by some authors the epistriatum. 

 They finally (in reptiles) become separated 

 and within each division in mammals sub- 

 ordinate "areas" with more or less char- 

 acteristic connections are differentiated. 

 The incompleteness of this differentiation 

 is responsible for much of the controversy 

 which has waged regarding the presence 

 and significance of loealizable cortical 

 areas. 



No cortical area can properly be de- 

 scribed as the exclusive center of a par- 

 ticular function. In higher mammals it is 

 true that the several final common paths 

 for particular effectors leave more or less 

 clearly defined areas of cortex and that the 



several kinds of sensory projection fibers 

 terminate in other more or less definite 

 areas. But these so-called sensory and 

 motor areas are in no proper sense centers 

 for the performance of definite functions. 

 Such a ' ' center ' ' is merely a nodal point in 

 an exceedingly complex system of cells 

 and fibers which must act as a whole in 

 order to perform any function whatso- 

 ever. Their relation to cerebral functions 

 is analogous to that of the railway stations 

 of a big city to traffic, each drawing from 

 the whole city its appropriate share of pas- 

 sengers and freight, and their great clin- 

 ical value grows out of just this segrega- 

 tion of fibers of like functional systems in 

 a narrow space, and not to any mysterious 

 power of generating psychic or any other 

 special forces of their own. 



The essence of cortical function is cor- 

 relation and a cortical center for the per- 

 formance of a particular function is a 

 physiological absurdity, save in the re- 

 stricted sense described above, as a nodal 

 point in a very complex system of associ- 

 ated conducting paths. Those reflexes 

 whose simple functions can be localized in 

 a single center have their mechanism 

 abundantly provided for in the brain 

 stem. 



In the broad view we may say that in- 

 telligence is a function of the cerebral cor- 

 tex, but only in the sense that here are 

 found the most complex correlations in the 

 chain of vital response whose initial phase 

 is to be sought in the environment which 

 supplies the stimulus and whose final 

 phase is also foiind in the changes wrought 

 in the environment by the bodily reaction. 

 A similar function is performed in a less 

 perfect way in lower animals which lack 

 the cerebral cortex, and doubtless even in 

 man the subcortical nervous apparatus 

 still plays an important part in all con- 

 scious processes. 



