PITHECUS RHESUS, iMACACUS RHESUS 371 



idea as to the relative size of the pyramidal system in maeaeus. Lying upon 

 the ventrolateral periphery is the circumferential zone, mesial to which is 

 the intermediate zone. Some external arcuate fibers, apparently arising in 

 the nucleus of Burdach, pass forward and inward to their decussation in 

 the median raphe. 



LEVEL THROUGH THE NHDDLE OF THE INFERIOR OLI\ ARV NUCLEUS (PIG. I 74) 



At this level, the addition to the inferior olive (10) ot the mesial and 

 dorsal accessory olives (DO, VO) is clearly shown. This level, however, is 

 more significant as again indicating the relative sizes of the three major 

 nuclear relay stations for discriminative sensibility, occupying the dorsal sen- 

 sory field. Thus the nucleus of Goll (NG) appears much smaller as com- 

 pared with the nucleus of Burdach (,NB), and the accessory nucleus of 

 Blumenau (NBI) (now showing some of its points of confluence with the 

 more mesial cell mass of Burdach). It offers an almost convincing argument 

 that the leg, foot and tail have been superseded in their sensory importance 

 by the development of the forclimb and particularly the hand. The relative 

 functional significance of the forclimb and hand, as represented by the nuclei 

 of Burdach and Blumenau ( N B, NBI ), when compared with the sensory 

 significance of the face and head, is clearly illustrated in the relatively small 

 size of the substantia gelatinosa trigemini (NR). 



The section also indicates the manner in which the internal arcuate 

 fibers, arising in the nucleus of Goll, sweep forward and inward as dense col- 

 lected bundles, skirting the ventral gray matter, while those arcuate fibers 

 arising from the nucleus of Burdach make their way by longer, more 

 graceful arcs, in less dense compact bundles, penetrating in their passage 

 the main mass of the reticular formation. Fibers of the twelfth nerve (N 12 ) 

 (nervus hypoglossus) make their way from their nucleus (Nhy) in the 

 ventral portion of the central gray matter to the inferior olivary nucleus 



