PHYSIOLOGY OF THE NERVOUS SYSTEM. 



722R 



see. After the removal of the deepest layers, 

 the animal lost completely the power of stand- 

 ing, walking, leaping, or flying. The power 

 had been injured by the previous mutilations, 

 but now it was completely gone. When placed 

 upon his back, he was unable to rise. He did 

 not. however, remain quiet and motionless, as 

 pigeons deprived of the cerebral hemispheres 

 do; but evinced an incessant restlessness, and 

 an inability to accomplish any regular or defi- 

 nite movement. He could see the instrument 

 raised to threaten him with a blow, and would 

 make a thousand contortions to avoid it, but 

 did not escape. Volition and sensation re- 

 mained; the power of executing movements 

 remained ; but that of coordinating those move- 

 ments into regular and combined actions was lost. 



Animals deprived of the cerebellum are in a 

 condition very similar to that of a drunken man, 

 so far as relates to their power of locomotion. 

 They are unable to produce that combination 

 of action in different sets of muscles which is 

 necessary to enable them to assume or main- 

 tain any attitudes. They cannot stand still for 

 a moment; and, in attempting to walk, their 

 gait is unsteady, they totter from side to side, 

 and their progress is interrupted by frequent 

 falls. The fruitless attempts which they make 

 to stand or walk are sufficient proof that a cer- 

 tain degree of intelligence remains, and that 

 voluntary power continues to be enjoyed. 



Rolando had, previously to Flourens, ob- 

 served effects of a similar nature consequent 

 upon mutilation of the cerebellum. In none 

 of his experiments was sensibility affected. 

 The animal could see, but was unable to exe- 

 cute any of the movements necessary for loco- 

 motion. 



Flourens' experiments have been confirmed 

 by those of Hertwig in every particular, and 

 they have been lately repeated with similar re- 

 sults by Budge and by Longet. The removal of 

 parl of the cerebellum appears capable of pro- 

 ducing the same vertiginous affection which 

 lias been already noticed in the case of deep 

 injuries to the mesocephale. After the well- 

 known experiments of Magendie, of dividing 

 either cms cerebelli, the animal was seen to 

 roll over on its long axis towards the side on 

 which the injury was inflicted. 



The effects of injuries to the cerebellum, ac- 

 cording to the reports of the experimenters 

 above referred to, contrast in a very striking 

 manner with those of the much more severe 

 operation of removing the cerebral hemispheres. 

 " Take two pigeons," says M. Longet; " from 

 one remove completely the cerebral lobes, and 

 from the other only half the cerebellum ; the 

 next day, the first will be firm upon his feet, 

 the second will exhibit the unsteady and un- 

 certain gait of drunkenness." 



Experiment, then, appears strikingly to fa- 

 vour the conclusion which Flourens has drawn, 

 namely, that the cerebellum possesses the power 

 of coordinating the voluntary movements which 

 originate in other parts of the cerebro-spinal 

 centre, whether these movements have reference 

 to locomotion or to other objects. 



That this power is mental, i. e. dependent 

 on a mental operation for its excitation and ex- 



ercise, is rendered probable from the experience 

 of our own sensations, and from the tact that 

 the perfection of it requires practice. The vo- 

 luntary movements of a new-born infant, al- 

 though perfectly controllable by the will, are 

 far from being coordinate : they are, on the 

 contrary, remarkable for their vagueness and 

 want of definition. Yet all the parts of the 

 cerebro-spinal centre are well developed, except 

 the cerebellum and the convolutions of the ce- 

 rebrum. Now, the power of coordination im- 

 proves earlier and more rapidly than the intel- 

 lectual faculties; and we find, in accordance 

 with Flourens' theory, that the cerebellum 

 reaches its perfect developement of form and 

 structure at a much earlier period than the 

 hemispheres of the cerebrum. 



It may be stated as favourable to this view of 

 the mental nature of the power by which vo- 

 luntary movements are coordinated, that, in 

 the first moments of life, provision is made for 

 the perfect performance of all those acts which 

 are of the physical kind. Thus, respiration 

 and deglutition are as perfect in the new-born 

 infant as in the full-grown man; and the exci- 

 tability of the nervous centres to physical im- 

 pressions is much greater at the early age, 

 partly perhaps in consequence of the little 

 interference which is received at that period 

 from the will. 



That the cerebellum is an organ favourably 

 disposed for regulating and coordinating all 

 the voluntary movements of the frame is very 

 apparent from anatomical facts. No other 

 part of the encephalon has such extensive 

 connections with the cerebro-spinal axis. It is 

 connected slightly indeed with the hemispheres 

 of the brain, by the processus cerebelli ad 

 testes, but most extensively with the mesoce- 

 phale, the medulla oblongata, and the spinal 

 cord. Now it is not unworthy of notice that 

 its connection with the brain proper is more 

 immediately with that part, which may be re- 

 garded as the centre of sensation; namely, with 

 the optic thalami. This connection of the 

 cerebellum with the centre of sensation may 

 probably have for its object to bring the mus- 

 cular sense to bear upon the coordination of 

 movements, in which the individual experience 

 of every one shows that that sense must mate- 

 rially assist. 



The cerebellum is brought into union with 

 each segment of the great nervous centre upon 

 which all the movements and sensations of the 

 body depend; through the restiform bodies it 

 is connected with the medulla oblongata and 

 the spinal cord ; by the fibres of the pons 

 with the mesocephale, and thus with the ante- 

 rior pyramids and corpora striata; and through 

 the processus e cerebello ad testes with the 

 optic thalami. What can be the object of 

 these extensive connections? It would be 

 difficult to conceive any function for which so 

 elaborate a provision would be more necessary, 

 than that of regulating and coordinating the 

 infinitely complex movements which the mus- 

 cular system is capable of effecting ; more 

 especially when it seems highly probable that 

 the antero-lateral columns of the cord, and the 

 anterior pyramids and olivary columns supply 



