868 



THE CENTRAL NERVOUS SYSTEM 



By studying these developmental differences in relationship to the activi- 

 ties of the muscular system, Bolk suggested that movement of those regions 

 of the body which are affected by muscle groups on both sides for example, 

 the head, neck or trunk would be represented on the cerebellar cortex by 

 an unpaired center that is, a center occupying a middle position and that 

 this would be capable of exercising an influence equally upon the muscles 

 of both sides. Movements of the limbs would require an entirely different 

 type of coordination, since they are not accustomed to act together, unless 

 for certain movements, as walking. Based on these theoretic considerations 

 Bolk found a definite correspondence to exist between the variations in the 

 development of certain cerebellar lobules and the functional importance of 

 certain muscle groups, and the general conclusions deducible from his and 



Fig. 223. Diagrams to represent respectively a ventral view of the left half and a dorsal 

 view of the right half of the human cerebellum illustrating the scheme of subdivision according 

 to Bolk. (From photographs of specimens from the Anatomical Museum, Western Reserve Medical 

 School.) (From Davidson Black J 



correlated work may be summed up as follows (cf. Davidson Black 16 ) : The 

 lobus anterior cerebelli (see Fig. 223) contains the centers for the coordi- 

 nation of the muscle groups of the head (eyes, tongue, muscles of mastica- 

 tion, muscles of expression), and of the larynx and pharynx. The lobus sim- 

 plex contains centers for the coordination of the muscles of the neck. The 

 lobulus medianus posterior contains the unpaired centers for the synergic 

 movements required by the right and left extremities for the purposes 

 of progression. On the other hand paired centers for the extremities 

 those centers that have to do with the independent movements of each limb 

 of the same side of the body are located in the lobuli ansiformes et para- 

 mediani (crus primum and crus secundum). The centers for the rest of 



