FUNCTIONAL ANALYSIS, CENTRAL AND PERIPHERAL G5 



that it comprises more than half the total weight of the brain, for 

 both cerebral and cerebellar cortices are derivatives of this pri- 

 mordial matrix, as will appear in the ensuing discussions. 



THE FUNCTIONAL SYSTEMS 



The preceding physiological analysis of the brain obviously rests 

 upon the peripheral relations of its several parts. The two primary 

 functions of the nervous system are, first, the maintenance of the 

 integrity of the individual, with efficient co-operation of parts among 

 themselves and with the total organization, and, second, the analysis 

 of experience and the translation of the sensory data into appropriate 

 behavior. The peripheral nerves are key factors in both these do- 

 mains. Our knowledge of the functional analysis of the cranial nerves 

 has been greatly increased during the last fifty years, largely by the 

 work of the so-called American school of comparative neurologists, 

 which I have recently reviewed ('43). 



Before I discuss the components of these nerves, a few definitions 

 are in order. In the attempt to envisage the nervous system from the 

 operational standpoint, distinctions have been drawn between sen- 

 sory correlation, motor co-ordination, and those central processes 

 that provide integration, and some measure of spontaneity of action 

 which might be grouped under the name "association" ('24c, p. 235; 

 '31a, p. 35). This classification is necessarily artificial, for all these 

 processes are interrelated. They interpenetrate, and they are not 

 sharply localized in the structural fabric. Nevertheless, these several 

 types of action are recognizable components of the unitary dynamic 

 system, and there are local differentiations of the structural organiza- 

 tion correlated with preponderance of one or another of them, more 

 clearly so in higher vertebrates than in lower. 



Sensory correlation, as the term is here employed, refers to inter- 

 action of afl^erent impulses within the sensory zone, that is, within the 

 field reached by terminals oi peripheral sensory fibers. The interplay 

 of these diverse afi'erent impulses takes two forms: (1) in fields of 

 undifferentiated neuropil, the activation of which results in altera- 

 tions of the central excitatory state or in mass movements of large 

 numbers of synergic muscles; (2) in more restricted areas (nuclei), 

 which activate the neuromotor apparatus of local reflexes. The mem- 

 bers of both groups are interconnected by systems of internuclear 

 fibers like the lemniscus systems, all within the sensory zone, so that 

 all activities of this zone interact one with another. These inter- 



