5o6 THE HIGHER ANTHROPOIDS 



in form. The nucleus of Burdach in its caudal c\tiemit\ , on the olliir hand, 

 appears as a definite extension from a dorsal prolongation of tlie central 

 gray matter, ll ])resents no detached prolongation into tiie surrounding 

 medullary substance. Its structural connection with the central gray matter 

 is much more decisive and appears in the iorm oi a compact, discretely cir- 

 cumscribed dorsal projection in this region, in this sense it has much the 

 same appearance of continuity in the gray matter as there is in the nucleus of 

 Rolando (substantia gelatinosa trigemini) (NR). In connection with the 

 nucleus of Goll there is no unpaired median nucleus oi Bischoll, which lact 

 again supports the idea that this median nucleus develops in connection 

 with the tail. 



The central gray matter fCen) is elongated laterally and stretches 

 as a narrow band along the \entral border of the dorsal sensory fields. It 

 contains at its center a small central canal, and extends laterally to become 

 continuous with the expanding dorsal horn now presenting itself in the form 

 of the substantia gelatinosa trigemini (NR) (the nucleus of Rolando). 

 This nucleus is in contact by its lateral margin with a collection of libers 

 constituting the descending trigeminal tract (Trd). Ventral to the 

 central gray matter are the decussating fibers of the pyramid (Pyx) 

 which \\n\v the appearance of compact bundles closely interlacing as they 

 cross from one side to the other. Their decussation separates the \ entral gray 

 column (Ven) from the central gray (Cen). The separation at this le\el 

 is not Cjuite complete as there still remain a few strands or bridges of gray 

 matter connecting the central gray w ith the \ entral gray column. Some idea 

 of the massiveness of the pyramidal decussation may be obtained m this 

 section. The mass of fibers affords an opportunity for estimating the xohime 

 of impulses necessary to the volitional control of the muscles. \ entral to the 

 substantia gelatinosa and on the ])eripherv of the axis is a dense collection of 

 fibers which produce a surface prominence, the spinocerebellar eminence 



