Mammalia: Nervous System 719 



works under the combined "direction" of the cerebral cortex and the 

 vestibular apparatus of the ear. But it does not initiate anything. 

 However it may be determined, its action is involuntary and does not 

 rise into consciousness. 



The brain and spinal cord are directly connected with only somatic 

 effectors, therefore controlling the striated muscles of the body-wall 

 and appendages but not directly controlling the smooth muscles of 

 the viscera, blood-vessels, and integumentary organs. These are under 

 immediate control of the autonomic nervous system, whose working is 

 involuntary. 



The distinction between "old" and "new" brain must not be 

 rigidly conceived. The cerebral cortex is not to be thought of as some- 

 thing "new" and important which has merely been added to an other- 

 wise unaltered "old" brain. By itself the cortex can do nothing. It 

 acquires importance only to the extent that it has nervous connections 

 with other parts of the brain. It works through, or by means of, the 

 reflex mechanisms. The establishing of these connections has necessi- 

 tated development of numerous associating and correlating centers 

 and tracts in various parts of the brain. However, these changes, 

 numerous and important as they are, do not in themselves materially 

 affect the external form and general anatomy of the "old" brain, nor 

 do they result in any profound change in the nature of its functions 

 so long as the functions are allowed to proceed without intervention of 

 the cerebral cortex. "Allowed" is the significant word. An animal with 

 an all-reflex brain is a mere robot. With a cerebral cortex super- 

 imposed on such a brain, the animal becomes a mechanism operated 

 by a driver who knows where he is going and whose choice of a road is 

 determined not merely by stimuli of the moment but by stored im- 

 pressions of what is past and remote. But it must not be assumed that 

 the fish with a non-nervous pallium is a robot. Even an earthworm can 

 learn a little something by experience — at least, it can modify its 

 reactions after repeated experiences — and unquestionably the most 

 stupid fish possesses a little capacity for modifying its behavior. It 

 must be conceded that the "old" brain of a teleost, with its non- 

 nervous pallium, admits of a little flexibility in behavior. Therefore 

 the cerebral cortex adds nothing of a new kind. What is "new" is 

 that the primitive nervously inert (presumably) pallium was taken 

 over as a site for the slow evolution of a complex structure through 

 which an originally feeble or latent capacity of the brain has been 

 elaborated and exalted into a dominant agency. Acquisition of nervous 

 function makes it a "new" pallium. 



The cerebellar cortex is "new" in so far as it has been developed 



