gio THE CEREBELLUM. 



" Muscular sense " is a complexus. By its processes, out of a 

 number of contributory impressions collected from various channels, 

 are synthesised specific perceptions. As in the physiological basis 

 of other senses, so here a number of impressions have, apart from 

 and devoid of psychical accompaniment, a reflex influence upon motor 

 (muscular) innervation. It is with this reaction that the cerebellum 

 is, it would seem, employed. That it is apparently devoid of psychical 

 accompaniment need not imply that the impressions concerned in it 

 are crude and inelaborate. The seeming want of reaction of so much 

 of the cerebellar structure under artificial stimulation, and the complex 

 relay system revealed in the histology of the cerebellum, suggest tbat 

 the impressions are elaborate. 



But the results of destruction of the cerebellum show plainly that 

 much co-ordination of muscles is possible in absence of the organ. The 

 ataxies of an apaesthetic limb and of the tabetic patient present in- 

 structive differences from cerebellar ataxy. In this latter, there is no 

 ignorance of the malpositions ; they are acutely recognised and even 

 anticipated. The dog prepares to lean against the wall to obviate the 

 fall that he expects will happen on that side. In the former ataxia 

 the malposition often remains unnoticed until attention is directed to it 

 by its falling within the central region of vision. The apoesthete and the 

 tabetic are without sensations which the decerebellate possesses, and to 

 the former deprivation of vision, a sense that contributes, not improbably 

 as importantly as the labyrinthine, to the co-ordination of innervation 

 requisite for equilibrium, means a severer loss. Hence Eomberg's 

 symptom — staggering on closure of the eyes — occurs with the former 

 but not with the decerebellate condition. The amount of recovery of 

 execution of movement possible to animals deprived of cerebellum is a 

 measure of the potency of the supplementary means for guidance of 

 muscular innervation ; many of these may be conscious. In decerebellate 

 animals a phenomenon regarding which observers are unanimous is the 

 profound lassitude which forthwith succeeds execution of movements 

 ordinarily quite unfatiguing. This is probably in large part a mental 

 fatigue, due to strained endeavour to continually obviate, or correct, 

 constantly recurring distortions of movements, keenly perceived at their 

 genesis to be imperfect. 



To sum up : the cerebellum is the organ rather of a particular class 

 of reactions than of a particular sense. Its reactions have their 

 sources in the sensifacient organs of various senses, but especially 

 of those pregnant with spatial quality, and in those subserving the 

 " muscular sense," in the widest meaning of that term. It supports 

 the tonus of the majority, perhaps of all, the cranio-spinal motor 

 root cells, of some more than others, e.g., those connected with 

 eye muscles, neck muscles, muscles of the spine. It preponderantly 

 helps to secure co-ordinate innervation of the skeletal musculature, 

 both for maintenance of attitude and for execution of move- 

 ments. So far as the geotropism and stereotropism of the animal 

 can be "centred" at any one limited field of the central nervous 

 system, that field is cerebellar. It supports habitual posture, and 

 is at least as importantly associated with the movements depend- 

 ent on the lower cerebral centres {e.g. walking, running), as with 

 those elaborated in connection with the highest {e.g. technical move- 

 ments). 



