THE CEREBELLUM. 625 



d mating the muscles of the general voluntary system causes the animal to 

 assume the most absurd and remarkable postures, which, to one accustomed 

 to these experiments, are entirely characteristic. Calling this want of equi- 

 libration, of co-ordination, of " muscular sense," an indication of vertigo, or 

 by any other name, the fact remains, that regular and co-ordinate muscular 

 action in standing, walking or flying, is impossible, although voluntary power 

 is retained. It is well known that many muscular acts are more or less auto- 

 matic, as in standing, and to a certain extent, in walking. These acts, as 

 well as nearly all voluntary movements, require a certain co-ordination of the 

 muscles, and this, and this alone, is affected by extirpation of the cerebellum. 

 It is true that destruction of the semicircular canals of the internal ear pro- 

 duces analogous disorders of movement, but this is the only mutilation, except 

 division of the posterior white columns of the spinal cord, which produces 

 anything resembling the results of cerebellar injury. 



When a portion only of the cerebellum is removed, there is slight disturb- 

 ance of co-ordination, and the disordered movements are marked in propor- 

 tion to the extent of the injury. After extirpation of even one-half or two- 

 thirds of the cerebellum, the disturbances in co-ordination immediately fol- 

 lowing the operation may disappear, and the animal may entirely recover, 

 without any regeneration of the extirpated nerve-substance. This important 

 fact enables one to understand how, in certain cases of disease of the cere- 

 bellum in the human subject, when the disorganization of the nerve-tissue 

 is slow and gradual, there may never be any disorder in the movements. 



If there be a distinct nerve-centre which presides over the co-ordination 

 of the general voluntary movements, experiments upon the higher classes of 

 animals show that this centre is situated in the cerebellum. If the cerebellum 

 preside over co-ordination, as a physiological necessity, the centre must be 

 connected by nerves with the general muscular system. If this connection 

 exist, a complete interruption of the avenue of communication between the 

 cerebellum and the muscles would be followed by loss of co-ordinating power. 

 From the anatomical connections of the cerebellum, it appears that the main 

 communication between this organ and the general system is through the 

 posterior white columns of the spinal cord. These columns are not for the 

 transmission of the general sensory impressions, and there is no satisfactory 

 evidence that they convey to the encephalon the so-called muscular sense. 

 When the posterior white columns are divided at several points, there is 

 want of co-ordination of the general muscular system. When the posterior 

 white columns are disorganized in the human subject, there is loss or impair- 

 .ment of co-ordinating power, even though the general sensibility be not af- 

 fecced, as in the disease called locomotor ataxia. 



Pathological Observations. Records of cases of lesion of the cerebellum 

 in the human subject have accumulated until the number is very large. A 

 study of cases in which the phenomena referable to cerebellar injury are not 

 complicated by paralysis, coma or convulsions, shows that serious lesion of 

 the middle lobe is almost always attended with marked muscular inco-ordina- 

 tion. Cases in which only a portion of one or of both hemispheres is involve:! 



