SUMMARY OF STRUCTURES 265 



to what may be called the medial cerebellar division. The nucleus dentatus 

 and nucleus emboliformis, occupying a more lateral position, are regarded as 

 constituents of the lateral cerebellar lobes. In the preceding descriptions 

 attention has been directed particularly to the nucleus globosus and the 

 nucleus dentatus. Reconstructions of these structures have indicated how 

 difficult It IS to make intrinsic distinctions between the medial and the 

 lateral nuclei. For this reason the dentate nucleus has been taken to include 

 both the nucleus dentatus and the nucleus emboliformis, while the nucleus 

 globosus includes the globosal and fastigial nuclei. 



The division of these nuclei into a medial and lateral group has much 

 functional significance. The lateral group is in large measure representative 

 of the appendicular muscles of the body, that is, the upper and lower extremi- 

 ties. That this group represents the appendicular muscles exclusively is not 

 the case; but the main expansions in the nucleus dentatus occur in response 

 to the progressive differentiation of motor capacity in the arms and 

 legs. 



THE DENTATE NUCLEUS AND ITS CONCURRENT EXPANSION WITH THE 

 CEREBELLUM AND CEREBRAL HEMISPHERES 



Inasmuch as the dentate nucleus is the principal relay station for 

 efferent impulses from the cerebellum, its significance in connection with this 

 organ as a whole becomes correspondingly important. From the physiologi- 

 cal point of view, it is fairly well established that conditions demanding 

 greater coordinative control of the musculature have their structural response 

 in definite expansions of the cerebellum. A comparison of different species of 

 mammals discloses the fact that the central or vermal portions of the cerebel- 

 lum have participated less in such development than the lateral lobes. This 

 is especially notable in the primates, in which the proportional size of the 

 cerebellar hemispheres in relation to the vermis progressively increases in 



