TARSIUS SPECTRUM 109 



ing some contributions from the internal arcuate libers arising in the 

 nucleus of Burdach (NB). By contrast, the extensive size of the posterior 

 longitudinal fasciculus (PL) and of the predorsal bundle ( PD) denotes 

 the importance of these colhculo-spinal and other midbrain connections. 



The central gray matter (Cen) is oval in outline and still more 

 dorsal in position. It contains in its center a much enlarged central canal, 

 while in its ventromesial area is the nucleus hypoglossus (Nhy). This 

 nucleus has none of the discrete distinction in its boundaries notable in the 

 higher primates. The emergent libers passing from it appear in larger and 

 coarser bundles than is the case in any other species examined. 



In a position dorsal to the central gray matter are the chief nuclei of the 

 dorsal sensory field. Their relation discloses the preponderance of the 

 nucleus of Burdach (NB) as compared with the nucleus of Goll (NG). 

 The large size of the nucleus of Rolando (NR) and of the descending 

 trigeminal tract (Trd) calls attention to the important role of the head 

 and face as a sensory director of the animal's locomotion. 



The outline of the dorsal aspect of the section shows an increasing con- 

 cavity due to the presence of the uvula cerebelli in this position. The fibers of 

 the spinal accessory nerve pass ventrolaterally through the nucleus of 

 Rolando (NR) toward then- pomt of emergence. The reticular torma- 

 tion (Ref) occupies the greatest portion of the section at this level. In 

 its lateral periphery is the nucleus ambiguus from which the emergent 

 fibers of the vagus nerve pass backward and inward toward the central 

 gray matter in the first part of their intramedullary course. The reticular 

 formation is further specialized to form the nucleus funiculus lateralis 

 and is penetrated by many long internal arcuate fibers. It is noteworthy 

 that these latter elements have none of the conspicuous appearance charac- 

 teristic of higher primates. They, like the mesial fillet and the pyramid of 



