CRANIAL NERVES 143 



sensibility, and probably the lateral-line organs also. Some proprio- 

 ceptive control is doubtless organized in the reticular formation of 

 the cord and bulb, but we have little information about how this is 

 done. From the entire sensory zone of these regions, proprioceptive 

 influence is filtered off and directed to the cerebellum, which is the 

 general clearing-house for these functions. Many vestibular root 

 fibers and a smaller number of trigeminal fibers go directly to the 

 cerebellum, and secondary fibers from the sensory zone enter it by 

 way of the spino-cerebellar tract and bulbar correlation tracts a and b 

 (p. 159; '44&). That exteroceptive and proprioceptive functions are 

 not completely segregated in these brains is shown by the fact that 

 many fibers of the spinal lemniscus (tractus spino-tectalis) send col- 

 laterals into the cerebellum ('14o, p. 376). Within the cerebellum the 

 general somatic sensory and vestibular components of the proprio- 

 ceptive system are locally segregated, the former in the body of the 

 cerebellum and the latter in the auricle, and this localization is a 

 primary feature of the cerebellum in all vertebrates, as Larsell has 

 shown. This author ('45) has also made it clear that cerebellar func- 

 tion includes much more than proprioception, or else the concept of 

 proprioception must be redefined in more inclusive terms. The second 

 alternative, I think, is better, as I have suggested in an article ('47) 

 on the proprioceptive system, from which some of the following para- 

 graphs are taken, by courtesy of the editor of the Journal of Nervous 

 and Mental Disease. 



Sherrington ('06, p. 347) defines the cerebellum as the head gan- 

 glion of the proprioceptive system, taking as the basis for his classifi- 

 cation of receptors "the type of reaction which the receptors induce." 

 In his exposition of this idea he makes it clear that the propriocep- 

 tive system is segregated from other sensory systems, not in terms of 

 the receptors involved but because the system as a whole exerts 

 regulatory control over the action of all skeletal muscles. The criteria 

 employed here are applied in the efferent, not the afferent, side of the 

 arc. In view of present knowledge of cerebellar function, Sherring- 

 ton's original concept of proprioception should be emphasized and 

 amplified. 



It has long been recognized that in the cerebellum of lower verte- 

 brates the sensory inflow is of two kinds, which are separately local- 

 ized, viz., (1) the vestibular and lateral-line systems in the lateral 

 part and (2) the spinal and trigeminal systems in the median body. 

 The second category traditionally comprises deep sensibility of sev- 



