144 THE BRAIN OF THE TIGER SALAMANDER 



eral sorts, notably that of muscle spindles, tendons, joints, and some 

 other internal end-organs. Current physiological research requires 

 radical revision and broadening of this traditional analysis. It has 

 been shown that in mammals different cutaneous areas, vibrissae, 

 audition, and vision have local representation in the cerebellum, as 

 do also various systems of synergic muscles. In lower vertebrates the 

 cerebellum has a broad connection with the hypothalamus, implying 

 representation in the cerebellum of olfactory sensibility also. 



In brief, cerebellar control of muscular movement employs prac- 

 tically all modalities of sense represented in the action system of the 

 animal. The function of the cerebellum as the "head ganglion of the 

 proprioceptive system" is not to pattern the muscular response (for 

 these functions are localized elsewhere) but to facilitate its execution ; 

 and this facilitation employs all available sensory experience. Many 

 organs of sense perform simultaneously both exteroceptive and pro- 

 prioceptive functions. Sherrington's fruitful analysis of the action 

 system into interoceptive, exteroceptive, and proprioceptive com- 

 ponents was not based upon the specificities of the receptive organs, 

 considered either anatomically or physiologically; but, on the con- 

 trary, the distinction was drawn in terms of what the animal does in 

 response to sensory excitations. The interoceptive systems are de- 

 fined in terms of internal adjustments, chiefly visceral. The extero- 

 ceptive systems are those which evoke adjustments of the body or its 

 members to events in the external world. The proprioceptive systems 

 are ancillary to the activities of the musculature in maintenance of 

 tonus, posture, and regulation of the action of synergic groups of 

 agonist and antagonist muscles in appropriate strength and sequence. 



Proprioception, therefore, must be defined not in terms of the 

 modalities of sense employed but in terms of the results achieved. 

 Cerebellar proprioceptive control is accomplished by the application 

 of all relevant types of sensory inflow to specific and successive mus- 

 cular activities which may be in process from moment to moment; 

 and the definition of "proprioception" must be formulated in terms 

 of the motor response rather than of the sensory systems involved. 

 The proprioceptive system, accordingly, includes all peripheral end- 

 organs and nerves and all central adjustors in the spinal cord, brain 

 stem, cerebellum, and cerebral hemispheres that collaborate in the 

 co-ordination and synergizing of muscular activity in process. In a 

 recent conference with Dr. Larsell he suggested to me that, in view 

 of the inadequacy of current conceptions of the true nature of the 



