238 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



side. The numerous sensory paths connected with the organ, es- 

 pecially those of the muscular sense, and those from the vestibular 

 nerve, suggest the view that in the complex cortex of the cerebel- 

 lum these afferent impulses act upon nervous combinations whose 

 discharges in turn are conveyed to the motor centers in a definite 

 and orderly sequence. Either point of view assumes that there 

 are in the cerebellum certain distinct mechanisms that is, combi- 

 nations of neurons that are essentially reflex centers, and that in 

 all of our more complex bodily movements these mechanisms 

 intervene. The second general set of theories regarding the cere- 

 bellum assumes that this organ is essentially the center or a center 

 for the muscle sense. This view is connected usually with the name 

 of Lussana,* but has been supported since in one sense or another 

 by many observers, f It is, in fact, not essentially different per- 

 haps from the second phase of the first group of theories. Those 

 who have expressed their idea of the physiology of the cerebellum 

 by saying that it is a center of the muscle sense have, in recent 

 times at least, recognized that this sense has a cortical center also in 

 the cerebrum. The view can not assume, therefore, a conscious 

 muscle sense mediated by the cerebellum, but only that fibers of 

 deep sensibility have a cortical termination therein, and that 

 the cerebellar activity thus aroused is in some way necessary to 

 the orderly adjustment of complex voluntary movements. Some 

 authors have assumed that the reflex effect thus exerted on the mus- 

 culature of the limbs and trunk is not concerned directly in elaborat- 

 ing the proper co-ordination of the muscles, but consists essentially 

 in the production of a state of tonus of a variable or adaptive char- 

 acter, which serves as a foundation, so to speak, for the volun- 

 tary control of the muscles. It would seem to be evident that on 

 any theory of this kind the results of cerebellar activity must be 

 exerted through some efferent channel upon the muscles concerned 

 in equilibrium and body-movements. No direct efferent path be- 

 tween the cerebellar cortex and the motor centers of the cord has 

 been established satisfactorily, but it may be that the indirect path 

 through the superior peduncles to the red nucleus and thence to the 

 cord through the rubrospinal tract subserves this function. Accord- 

 ing to another point of view, the cerebellum is a great augmenting 

 organ for the neuromuscular system. It is added on, as it were, to 

 the cerebrospinal motor system, and serves not to co-ordinate the 

 motor discharges, but to increase their strength or effectiveness. 

 This general view, first proposed by Weir Mitchell (1869), has been 

 supported by Luys, and especially, although with important 



* Lussana. See "Journal de la physiol. de 1'homme," 5, 418, 1862. 

 t See Lewandowsky, "Archiv f. Physiologie," 1903, 129. 



