no THE LOWER PRIMATES 



tarsfus, indicate a less highly organized condition in discriminative sensi- 

 bility and vokintary motor control. 



It seems obvious from the known behavior of the animal that its range 

 of skilled movements is comparatively limited. From these structures in the 

 brain stem it is permissible to conclude that tarsiers in general accjuire but 

 little increase in their motor attainments under the influence of training. 

 This level might well pass for the corresponding region in the cat or rabbit; 

 in fact, its components have a close resemblance to marsupial organization. 

 The medullary substance in the intermediate zone contains the rubrospinal 

 and spinothalamic tracts (Rst, Spt), while on the circumference are the two 

 ascending cerebellar fascicles (Fie, Gow). 



A small collection of gray matter dorsal to the main body of the olive is 

 the dorsal accessory olivary nucleus (DO). 



LEVEL THROUGH THE MIDDLE OF THE INFERIOR OLIVARY NUCLEUS (fIG. 54) 



At this level the inferior olive is conspicuous because of its structural 

 inferiority as compared with other species. Tliis nucleus in tarsius consists 

 of an aggregation of gray matter, so poorly differentiated from the formatio 

 reticularis that it might appear as an intrinsic part of this formation. The 

 portion of the nucleus which may be discerned appears to correspond to the 

 mesial accessory olive in other forms. A very small mass of cells lateral to 

 this structure represents the inferior olive itself. Thus the most conspicuous 

 portion of the nucleus seems to represent what is usually described as the 

 paleo-olive. Compared with either the cat or the rabbit, the olive in tarsius is 

 distinctly more primitive, and this certainly is the case in comparison with 

 all other primates. Judged alone by the criteria of this structure, it would 

 seem that the tarsier occupies a low position in the organization of its central 

 nervous system; one which might, however, serve most advantageously as a 

 fairlv unbiased foundation for extensive further modifications. In the inter- 



