The Lower Puiiion of the Uiunun Braiu-Slcin. 45 



nuclei. Its ventral border (figure 2), overlying laterally the dorsal termina- 

 tions of the pontine wall, shows a curving with the convexity dorsal. The 

 superior border winds about the cephalic ventral angle of the superior 

 vestibular nucleus and then projects mesially along the straight ending of 

 the latter nucleus on the dorso-lateral plate. From the cephalic ventral 

 angle of the superior ^'estibular nucleus, to the termination of the model, 

 the lateral wall of the fifth nucleus is marked by an irregular lateral pro- 

 jection. This is due to the sudden widening out of the sensory reception 

 nucleus which caps the superior end of the substantia gelatinosa. The 

 expansion shows laterally (hgure 2) as a corrugated and notched projection 

 cephalic to the dorsal i>]n\v at the superior end of the vestibular nucleus, 

 and extends cephalad to the limit of the model. It is placed at first at some 

 distance laterally from the brachium conjunctivum, but it approaches the 

 ventral lateral margin of this very soon and sends a short dorsal spur around 

 its lateral and dorsal margin. This is shown at the extreme limit of the 

 model (figures 2 and 3). The lateral surface passes insensibly into the 

 smooth and extensive dorso-lateral plate of the nucleus, except at the cephalic 

 limit of the cell-mass, where the surface passes over the dorsal spur. The 

 dorsal-lateral plate (figure 3), underlying ventrally the brachium conjunc- 

 tivum, is practically smooth throughout. Its mesial border is somewhat 

 irregular, but it shows caudally a rather rapid mesial curvature, which 

 becomes very mild in the cephalic portion of the model. 



The ventral surface of the dorso-lateral plate is fairly smooth, and the 

 plate is much thicker transversely just cephalic to the upjjer limit of the 

 superior vestibular nucleus. This thickness reaches its maximum in the 

 lateral angle of the ventricle, where it exists as a marked rectangular ridge. 

 As one passes forward, the dorsal and ventral surfaces of this ridge approxi- 

 mate and the ridge merges into the thickened triangular plate. This 

 thickened triangular plate has its base in the caudal, thickened portion of 

 the dorso-lateral plate and extends cephalad, with its dorsal edge overlying 

 mesially the ventral surface of the dorso-lateral plate, to terminate by 

 ventral deflection in the column of the nucleus motorius princeps nervi 

 trigemini. The rectangular column is composed of large polygonal cells 

 closel}^ grouped together in its caudal extremity, but as it loses its character 

 cephalad these cells disappear from it. 



From mesial view (figure 4) the chief motor nucleus of the fifth nerve 

 is seen to begin as a marked caudal spur which lies mesial to the cephalic 

 portion of the superior vestibular nucleus. This spur is composed of fairly 

 large cells. Traced cephalad the spur expands in the transverse diameter, 

 but especially in the dorso-ventral direction. This expansion occupies the 

 whole mesial surface of the nucleus as the superior vestibular nucleus termi- 

 nates. It shows a wide, gentle, mesial prominence as the nucleus meets 

 with the lateral wall of the nuclei pontis, ventral to which prominence the 

 wall slopes laterally and ventrally. This prominence gradually subsides as 



