CHAPTER VI 

 PHYSIOLOGICAL INTERPRETATIONS 



APPARATUS OF ANALYSIS AND SYNTHESIS 



IN A primitive brain like that of Amblystoma the stable framework 

 of localized centers and tracts performs functions that are pri- 

 marily analytic. The sense organs are analyzers, each attuned to 

 respond to some particular kind of energy. The sensory systems of 

 peripheral nerves and the related internal sensory tracts are parts 

 of the analytic apparatus, in so far as their functional continuity 

 with the peripheral organs of the several modalities of sense can be 

 traced. 



On the motor side similar conditions prevail. The neuromotor 

 apparatus is organized in functional systems, each of which is 

 adapted to call forth the appropriate sequence of action in a par- 

 ticular group of synergic muscles. These units are as truly analyzers 

 as are those of the sensory systems, though in an inverse sense. Out 

 of the total repertoire of possible movements, those, and only those, 

 are selected which give the appropriate action. The efferent fibers are 

 grouped, the members of each group being so bound together by 

 central internuclear connections that they act as a functional unit 

 adapted for the execution of some particular component of behavior, 

 such as locomotion, conjugate movements of the eyeballs, seizing and 

 swallowing food, and so on. 



The several sensory systems are so interconnected within the sen- 

 sory zone as to react mutually with one another. They form a 

 dynamic system so organized that all discharges from this zone are 

 resultants of this interaction. This interplay has pattern. The various 

 modalities of sense are not discharged into a single common pool of 

 equipotential tissue. The sensory components of the nerves are segre- 

 gated, more or less completely, so that related systems converge into 

 dominant centers of adjustment— exteroceptors in the tectum, pro- 

 prioceptors in the cerebellum, olfacto-visceral systems in the hy- 

 pothalamus, olfacto-somatic systems in the habenula, and so on. 



A review of the internal architecture of the adult brain of Amblys- 

 toma suggests that the specifications of the general plan are drawn 



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