Tlic Lower Poiiion of (lie Human Brain-Stcin. 15 



toward the pontine nuclei, until the lateral wall of the pons project.s far 

 (lorsally. Both of these i)roj('('tions arc very irregular and are cut by fiber 

 bundles coursing through them and by spurs and hssures on their surfaces. 



As the lemniscus medialis changes its long axis to a transverse position, 

 the character of the ventral wall of the formatio reticularis changes. The 

 mesial ventral projection is suddenly discontinued, but the deep dorsal 

 fissure lietween the two projections continues almost to the cei^halic bortler 

 of the model. This ventral surface of the formatio, lying dorsal to the 

 lenniiscus medialis, is roughened by slight eminences and shallow groovings. 

 Mesiallj' it is encroached upon by th(> nucleus reticularis tegmenti pontis. 



THE INDIVIDUAL MASSES OF GRAY MATTER. 

 NUCLEUS FASCICULI GRACILIS. 



From its inferior end, just caudal to the lower extremity of the decus- 

 satio ])yramidum, the nucleus fasciculi gracilis extends as a continuous 

 nuclear mass to the inferior end of the nucleus vestibularis medialis a point 

 on the same level with the mid-iioiut of the nucleus alse cinerea>. It measures 

 in the longitudinal direction 14.4 millimeters. The whole extent of the 

 nucleus igr) is shown in figure 3, a dorsal view, while figure 4 gives the mesial 

 view. Figure 9, a characteristic transverse section through the decussation 

 of the pyramids, shows the extent and characteristics of the nucleus in its 

 caudal half, while figure 10 gives a transverse section through its broader and 

 larger cephalic half. 



In its caudal portion the nucleus lies in the midst of the fiber bundles 

 of the fasciculus gracilis, but the fasciculus becomes smaller above and the 

 nucleus correspondingly larger, so that this nuclear mass occupies the whole 

 of the mesial dorsal segment of the medulla (figures 3 and 10). On the mesial 

 surface the dorsal longitudinal fissure is in close approximation in the lower 

 two-thirds of the nucleus, but in the cephalic portion the mesial surface is in 

 relation particularly to the caudal half of the nucleus alae cinereae. Lateral 

 to this gracile nuclear mass are the fibers of the fasciculus cuneatus for the 

 caudal five-sixths of its extent, but in its more cephalic portion the cell-mass 

 of the nucleus fasciculi cuneati is directly lateral to it. W'ntral to the nucleus 

 lies the central gray matter of the cord in its lower two-thirds; in the cephalic 

 one-third are the nucleus alse cinereae and the fasciculus solitarius with its 

 accompanying lateral nuclear mass. These relations are brought out in the 

 transverse sections already referred to and in the figures showing the dorsal 

 and mesial surfaces of the model. 



The dorsal aspect of the nucleus fasciculi gracilis, when reconstructed, 

 shows as a long mass, with the caudal half narrow and gracile while the 

 cephalic half broadens out in the clava (figure 3). This increase in the 

 transverse diameter of the nucleus is rather sudden and occurs at the cephalic 

 limit of the decussatio pyramidum. The most caudal portion of the nucleus 



