TARSIUS SPECTRUM 103 



accessory nerve, and the large dimensions of the vestibular area. These 

 features will be especially dealt with in the interpretation of their physiologi- 

 cal significance. 



LEVEL OF THE PYRAMIDAL DECUSSATION (piG. yl) 



At this level the characteristic feature is the crossing from one side to the 

 other of pyramidal fibers (Pyx). This is much less regular than in other 

 primates. The crossing strands arc somewhat indiscriminate in their disposi- 

 tion. The bundles tend to interlace and have little of that successive crossing 

 first from one side and then from the other, notable in higher primates. There 

 is a suggestion, particularly at the caudal end of the decussation, that some 

 fibers may make their way into the dorsal columns after the manner of certain 

 lower mammals. This observation needs experimental confirmation. Pal- 

 Weigcrt preparations scarcely more than suggest this possibility. In all 

 details the pyramidal crossing seems more primitive than in any other pri- 

 mates. If some fibers actually do enter the dorsal columns, the conception 

 of tarsius as a much generalized intermediate form gains further support. 

 The central gray matter (Cen) is large and rectangular in outline, con- 

 taining near its center the central canal. Its greatest diameters are in the 

 antero-posterior direction. It is connected with a large dorsal gray column 

 by a cervix of somewhat irregular outline, but separated from the ventral 

 gray column by the crossing pyramidal fibers which assume a juxtagriseal 

 position in dense bundles after they have decussated. The large size of the 

 ventral gray column (Ven) is notable, particularly as there appear to arise 

 in it many fibers which take a course backward and outward, characteristic 

 of the spinal accessory nerve. These fibers constitute a nerve of much larger 

 size and generally more conspicuous than in any of the apes. This fact, in 

 conjunction with the great prominence of the ventral gray column, suggests 

 the probable specialization in connection with one of the peculiar habits of 



