TARSIUS SPECTRUM 117 



Both of these conditions are in closer accord with the subprimate mammals 

 than with the Anthropoidea. 



Mesial to the facial nucleus is a disseminated collection of axons reach- 

 ing backward toward Deiters' nucleus. These form the beginning of the 

 Deiterso-spinal tracts (DT). Immediately dorsal to the posterior longi- 

 tudinal fascicuhis is the caudal extremity of the nucleus abducentis 

 (Nab). The predorsal bundle (PD) is large and indicates to what 

 degree tlie annual depends on its automatic movements. This observation 

 becomes more significant in view of the small size of the pyramid which calls 

 attention to the relatively meager control of voluntary movement possessed 

 bj" tarsius. The mesial fdlet (Mf) occupying a position dorsal to the 

 pyramid, denotes a low degree of discriminative sensibihty in the animaL 



All of these facts collectively signify an animal of a simple motor organi- 

 zation and extremely limited in such behavior as is conditioned by learning 

 and imitation. 



LE\'EL OF THE CEREBELLAR NUCLEI (fIG. 57) 



Characteristic features at this level are the appearance of the heavy 

 bundles constituting the intramedullary portions of the sixth and seventh 

 cranial nerves (N6, N7). The fibers of the vestibular division of the eighth 

 nerve make their way to Deiters' nucleus between the restiform body 

 (ICP) and the descending trigeminal tract (Trcl). Some fibers of the 

 acoustic division ( N8 ) of the eighth nerve appear in relation to the tubcrcu- 

 him acusticum (Tub). The fourth ventricle is still further reduced in 

 size. Its roof is formed by the median portion of the cerebeHum in which 

 is situated the roof nucleus (Nfg). Heavy bundles of fibers entering the 

 juxtarestiform body pass backward and inward from Deiters' nuckms to 

 the nuck'us of the roof. Lateral to these fibers in the median vestibule of the 

 cerebelkim is a collection of gray matter forming the nucknis dentatus and 





