44 A Reconstruction of the Nuclear Masses in 



surface is overlaid by the lateral plate of the nucleus of Blumenau already 

 described (figure 10). As this lateral plate recedes from its surface, the 

 substantia is characterized by a smooth notch on its ventral surface, followed 

 by a ventral projection toward the middle of the nucleus lateralis, and slightly 

 superior to these by a sharp dorsal spur. Figure 2 gives these markings. 

 The mesial surface throughout this extent is quite smooth and rounded. 

 The long axis of the oval still continues in the dorso-ventral direction. This 

 portion of the substantia, lying caudal to the cephalic pole of the nucleus 

 lateralis, shows but a slight lateral deflection. Just at the level of the 

 cephalic }3ole of the nucleus lateralis and mesial to the main ]:)ortion of the 

 nucleus ambigims, the substantia gelatinosa becomes quite thin, with the 

 maintenance of the dorso-ventral direction of the long axis (figure 11). 

 It takes a slight, rather abrui)t, mesial bend at this point, to be succeeded 

 quickly by a lateral deflection. These clianges in direction of the main 

 axis of the nucleus can be made out in flgure 4. From this point, cephalad 

 to its termination in the main sensor}^ dilatation of the nucleus, the sub- 

 stantia continues the dorso-lateral deviation of its cephalic course by a series 

 of slight mesial and lateral deflections similar to those just described. 



Around the cephalic end of the nucleus tractus solitarii, the mesial 

 surface of the substantia gelatinosa jirojects dorsally and somewhat mesiall.y, 

 to join with the ventral surface of the nucleus nervi vestibuli medialis 

 (figures 4 and 12). Just superior to this dorsal projection there occurs a 

 circumscribed deeji depression, which is boimded ventrally by a rounded 

 edge. The substantia just cephalic to this is raised in a gradual but marked 

 mesial eminence. The oval of the substantia continues upward, bending 

 somewhat laterally as it passes the nucleus nervi facialis. In this region 

 the long axis of the oval becomes more oblique as its ventral edge is moved 

 laterally. Its dorsal margin joins with the nucleus nervi vestibuli superior 

 by large bridges of tissue (figure 13), which intermit in places. In the 

 region of the su]Derior portion of the nucleus of the seventh nerve the sub- 

 stantia gelatinosa becomes very irregular; it decreases in size and is broken 

 by many fiber bundles as they course through it in all directions. Con- 

 tinuing ventrally to the cephalic end of the nucleus nervi vestibuli superior, 

 it merges with a lateral sheet of cells which lies ventral to the most ventro- 

 lateral portion of the superior vestibular nucleus. The fusion of the sub-i 

 stantia gelatinosa with this lateral nucleus of the complex takes place at 

 the level of the superior pole of the seventh nucleus, slightly cephalad to 

 the caudal origin of the lateral sheet of cells. From this point cephalad 

 to the termination of the model, the nucleus may be described as a lateral 

 portion and the median motor portion, the nucleus motorius princeps nervi 

 trigemini. 



When viewed from the lateral surface the nucleus of tlie fifth nerve 

 shows as an irregular mass placed between the ventral border of the superior 

 vestibular cell-mass and the dorsal jjorder of the lateral wall of the pontine 



