SUMMARY OF STRUCTURES 



269 



Longitudinal Coefficients of the Nucleus Dentatus and Nucleus Globosus 

 IN Lemur, Tarsier, Marmoset and Mycetes 



Although the diftcrcnccs in these species arc not so stril:ing as in the 

 higher primates, they are sufficient to indicate that an evohitional process 

 has impressed its influence upon the chief cerebellar nuclei. 



THE NUCLEUS RUBER 



The nucleus ruber of the midbrain, which is the principal relay station 

 between the cerebelhim and the spinal cord, is particularly sensitive to cere- 

 bellar expansion. It thus oflers a reliable index of augmentation in coordina- 

 tive control over the muscles. Since the red nucleus receives impulses directly 

 from the nucleus dentatus, the increments in the former should be propor- 

 tional to those in the latter. In other words, if there does occur an actual 

 increase in the coordinative control arising from the cerebellum both the 

 dentate and the red nuclei should show increments of expansion in their 

 coefficients pari passu. That such is not the fact, either in the lower primates 

 or in the primate series as a whole, calls for explanation. In comparing the red 

 nucleus in the lower primates, there is a progressive rise from the lemur to 

 mycetes. This increase is so pronounced as to leave little cjuestion of a 

 progressive expansion in this nuclear structure of the midbrain. The longi- 

 tudinal coefficients likewise show a corresponding increment in the nucleus. 



