SUMMARY OF STRUCTURES 267 



The dynamic significance of the suprasegmental divisions of the nervous 

 system has ah-eady been mentioned in rehition to the actual and potential 

 expansions of the brain. Such expansions provide further opportunity for 

 increasing the range and number of neural syntheses in the progressive 

 adaptations of animal behavior. To find the dentate nucleus expanding con- 

 currently with the lateral hemispheres of the cerebellum and the cerebral 

 hemispheres reflects the tendency of this nucleus to participate in the progres- 

 sive development of behavioral adaptation. For this reason, the nucleus may 

 be accepted as a reliable index of the coordinative adaptability of the animal. 

 Its size, proportions and definition may, to an extent at least, be taken to 

 indicate the range and intricacy of behavioral adjustments of which an ani- 

 mal is capable. 



Connections of the Dentate Nucleus. As the gateway of impulses 

 passing out of the cerebellum, the nucleus dentatus has its major connection, 

 by way of the superior cerebellar peduncle, with the red nucleus m the mid- 

 brain. This latter structure acts as an intermediate relay for the conduction 

 of impulses through the axis to their various levels of distribution in the brain 

 stem and spinal cord. The course of the fibers constituting the superior cere- 

 bellar peduncle need not be considered in detail further than to observe that 

 by means of two major decussations, both of which occur in the midbrain, 

 the final connection between the dentate nucleus and the muscles is ipsilateral. 

 In this way, the dentate nucleus on one side distributes the impulses from 

 the cerebellum to the musculature of the corresponding side of the body. 

 Acting thus in the capacity of the chief efferent distributing station in the 

 cerebellum, the dentate nucleus is connected by means of cortico-dentate 

 fibers with areas in the lateral lobes of the cerebellum as well as in the vermis. 

 Syntheses of coordinating impulses arising in the cortex of the vermis and the 

 lateral lobes thus make their way to the dentate nucleus and here find an 

 outlet for their stabilizing influence over the muscles of the body. 



