THE CEREBELLUM 611 



which follow extirpation of the membranous labyrinth of the internal ear 

 (cf. page 476), and the inference seems not too far drawn that the business 

 of the cerebellum consists in part in the physiological elaboration of impulses 

 contributed to it by the vestibular nerve. 



In so saying we do not wish to assert that the labyrinth acts exclusively on 

 the cerebellum, or that the cerebellum receives impulses only from the labyrinth, 

 for other observations make such a view quite untenable. 



Eecently Marburg has cut the lateral cerebellar tract in the cord of a dog 

 at the level of the second cervical segment. After a bilateral operation, sway- 

 ing movements appeared both in walking and in standing, the legs were placed 

 and held in abnormal positions, the pelvis was abnormally inclined and the spine 

 abnormally curved. Voluntary movements, tonus of the muscles, sensibility of 

 the skin and the general strength of the animal appeared to be unaffected. 



These disorders are doubtless due to the absence of certain afferent im- 

 pulses coming from the locomotor organs, and the idea of Lussana, recently 

 taken up and developed by Lewandowsky, that the symptoms following in- 

 juries to the cerebellum are really to be interpreted as a derangement of the 

 muscular sense, might not be so far amiss as Luciani supposes. 



No claim is made that the cerebellum constitutes the only center of the 

 muscular sense, nor is there anything to prove that the conscious processes 

 depend upon it, for plenty of other facts show with perfect clearness that the 

 sensations of motion and position are present after the cerebellum has been 

 removed, also that they are profoundly influenced by destruction of certain parts 

 of the cerebral cortex when the cerebellum is uninjured. 



The impulses brought to the cerebellum by the above-named pathways and 

 by other fibers are elaborated in that organ by some process which, so far as 

 we know, is independent of consciousness. At any rate the fibers leaving the 

 cerebellum are the medium of some influence which increases the potential 

 energy (sthenic activity) of the neuromuscular mechanisms, and the degree 

 of their tonus (tonic activity) during functional pauses. It also quickens the 

 rhythm of the impulses while the mechanisms are active and causes these 

 impulses to be so fused and regulated that they eventuate in harmonious move- 

 ments of the proper extent, intensity, etc. (static activity). 



Against this formulation of the cerebellar functions, which Luciani makes 

 in summing up the effects of extirpation, different objections have been urged 

 by certain authors, who wish to regard the cerebellum as the seat of the muscular 

 sense, the organ for the maintenance of equilibrium, or for the coordination of 

 certain muscular movements. Since these views are not out of harmony with 

 the facts, it seems to the author that they are not inconsistent with Luciani's 

 position, but that they differ from his view rather in the mode of expression than 

 on fundamental grounds. 



Thomas, who has attempted to analyze the regulating influence of the cere- 

 bellum still more closely, gives, among others, the following example of its action. 

 When the fore foot is lifted voluntarily from the ground, the impulse from the 

 motor cortex of the cerebrum extends not only to the necessary muscles, but by 

 a special pathway it excites also the cerebellum to send out impulses which 

 increase the tonus of the adductor and trunk muscles of the same side. But 



