LEMUR MONGOZ 53 



coordination. TIic nucleus may be, as in this instance, an irregular, diffuse 

 mass of gray matter, or it may present itself as a complexly convoluted 

 structure whose convokitions serve to increase its functional capacity. An 

 animal having a small dentate nucleus should be capable of a relatively 

 limited range of highly coordinated acts. It is of interest to note that in 

 lemur this nucleus is neither well defined nor extensive in size, from which 

 it may be inferred that the degree of coordinative control dependent upon 

 the cerebellum is relatively less in this animal than in some of the higher 

 primates. 



Mesial to the dentate nucleus is another aggregation of nerve cells. 

 This is the nucleus Jastigii (Nfg). By means of fibers constituting the 

 juxtarestiform body (Cjr), it is connected with those nuclei in the floor 

 of the fourth ventricle which receive impulses from the semicircular 

 canals, utricle and saccule. The nucleus fastigii is, therefore, a structure 

 intimately concerned with the function of balancing and may be regarded as 

 one of the higher elaborating stations for equilibratory control. Its compara- 

 tively large size in lemur has a significance similar to that of the large nuclei 

 of Schwalbe and Deiters, unquestionably indicating the great need on the 

 part of the animal for a highly organized balancing control. 



It is presumed that functionally the vermis (Ver) is concerned 

 with the maintenance of coordinative control of the axial and paraxial 

 musculature of the body. This is a portion of the cerebellum which manifests 

 the greatest phyletic constancy, whereas the lateral lobes, because they are 

 functionally related to the muscles of the extremities, vary according as the 

 upper and lower extremities arc capable of more or less complex perform- 

 ances. Another feature at this level is the trapezoid body (Trp), and 

 adjacent to it the trapezoid nucleus (Ntr). The trapezoid body is situated 

 immediately dorsal to the pyramid (Py ) and consists of a complex system 

 of decussating fibers. These crossing libers represent the decussation in the 



