FUNCTIONS OF THE CEREBELLUM. 903 



been supposed to be developed in connection with the part played by the 

 limbs in locomotion. But their absence in birds and frogs and their remarkably 

 large development in the Cetacea negatives such a view ; the experiments above 

 related have moreover shown that the vermis is connected with limb as well 

 as with trunk muscles, and the lateral lobes with the trunk as well as with limb 

 muscles. The deduction has been made, that size of cerebellum is related 

 to degree of locomotivity. But the smallness of the frog's cerebellum is 

 against that. Its size does, however, seem connected with range and variety 

 of movement in some way ; the cerebellum of the albatross is very large among 

 birds. On the whole the suggestions given by mere gross anatomy have been 

 in the case of the cerebellum more than usually unfortunate. 



In the development of the organ it is interesting that even the azygoid 

 median lobe makes its appearance as a pair of lateral structures. Further, that 

 the organ is by its ontogeny a portion of the sensory region of the neural tube. 

 Histological completion of its tissue, to judge by date of myelinisation, occurs 

 first in the vermis and in the flocculi, 1 and is in the lateral lobes very much 

 later ; this agrees with the late appearance of the lateral lobes in the phylo- 

 genetic history of the organ. 



Functions of the cerebellum.— It remains to attempt to form a 

 conception of the functions of the cerebellum. For such an attempt 

 two steps are to be taken : the tracking down the fundamental mischief 

 at the root of tbe raw "symptoms" catalogued above; the drawing 

 from this mischief inferences regarding the share taken by the cere- 

 bellum in the work of the nervous system. 



The former problem may best be attempted by discussing an able 

 analysis offered by Luciani. As first pointed out by Flourens, injury 

 of the cerebellum causes inco-ordination of movement — ataxia. Much 

 of the clumsiness of movement of the first (ten) days after cerebellar 

 injury, Luciani ascribes to the tonic spasm existent in certain muscles, 

 or, if not actually existent, liable to appear at the moment of active 

 innervation. This tonic spasm and overaction renders certain groups 

 of musculature unmanageable. This spastic rigidity affects especially 

 the lateral and extensor muscles of the trunk and neck, and the extensor 

 and abductor muscles of the fore-limbs (dog ; in monkey the flexors 

 and adductors). 2 The more permanent inco-ordination evident after 

 the period of rigidities has passed is considered by Luciani to be 

 associated with, and probably due to, three defects of neuro-muscular 

 action, namely, to parasthenia 3 or defective force, paratonia or defective 

 tone, and to astasia or unsteadiness of contraction. The three defects 

 accompany each other, and affect, after total ablation of the cerebellum, 

 the muscles of tbe body everywhere (Luciani), but predominantly 

 the muscles of the loins and hind-limbs, and the muscles fixing the 

 head. 



Concerning the parasthenia, Luciani points to his direct dynamo- 

 metrical observations ; he found, e.g., the movements of the homonymous 

 limbs weaker than those of the crossed side ; his dogs in swimming 

 circled toward the crossed side, although in walking they deviated 

 toward the homonymous side. 



Concerning the paratonia, Luciani points to the slackness of the 



1 Alexander Bruce, Brain, London, 1895, vol. xviii. 



2 Luciani, Ferrier, and Turner, loc. cit. 



3 Luciani has applied the full negative in his nomenclature, hut as he does not use the 

 terms in the sense of complete deprivation, I venture here to modify his "asthenia" and 

 " atonia" to "parasthenia" and " paratonia." 



