430 



PHYSIOLOGY 



CHAP. 



these two fibre -systems is in proportion with the injury of that 

 nucleus. Lesions of the nucleus fastigii produce no degeneration 

 in the cord. 



Besides Marchi's bundle, another efferent cerebello-spinal tract, 

 mostly crossed, but to a small extent direct, has been described 

 by Mingazzini, Pick, and others. The crossed portion leaves the 

 internal segment of the restiform body, enters the raphe as 

 internal arcuate fibres, joins the external ventral arcuate fibres 

 of the opposite side, and enters the pyramidal tract (Fig. 228, c, d). 



The few uncrossed fibres 

 pass as external ventral 

 arcuate fibres and join 

 the pyramid tract on the 

 same side (Fig. 228, e). 

 It is evident that the 

 crossed portion, since it 

 decussates again with the 

 contralateral pyramid, 

 joins each lateral half 

 of the cerebellum and of 

 the same side of the 

 cord, and that the small 

 uncrossed portion, which 

 also decussates with the 

 homolateral pyramid, 

 establishes a relation be- 

 tween each lateral half 

 of the cerebellum and 

 the opposite side of the 

 cord. This is clear from 

 Fig. 231. 



II. The experimental 

 determination of the 

 functions of the cere- 

 bellum is one of the 

 most difficult problems in the physiology of the central nervous 

 system. We devoted many years (1884-91) to experiments 

 in the solution of this question. Previous investigators had 

 confined themselves almost without exception to ascertaining 

 the immediate effects of lesion or partial removal of the cere- 

 bellum or its peduncles. Eolando (1809) contented himself 

 with destroying half or the whole of the cerebellum in different 

 mammals, and giving a summary description of the effects on 

 the same day, without taking any trouble to keep the animals 

 alive. Fodera (1823) and, shortly after, Flourens (1824-42) 

 observed, particularly in birds, the immediate effects of small suc- 

 cessive ablations of increasingly deeper layers of the cerebellum. 



FIG. 231. Diagram to show crossed (a) and direct (l>) cere- 

 bello-spinal paths which accompany pyramidal tract p, 

 and are in relation with the cells of the ventral horn 

 ca, from which the motor roots ra emerge to inner- 

 vate the muscles m. (Mingazzini.) 



