The Lower Portion of the Human Brain-Stem. 43 



complex pertaining to the fifth nerve is necessarily incomplete, but it is 

 included for the purpose of describing as much of the complex as exists in the 

 model. The course and morphology of the substantia gelatinosa is practicall}' 

 complete in the extent of the model, and its description and relations should 

 have value. 



The substantia gelatinosa Rolandi is that long nuclear mass, extending 

 from the upper cervical cord to the middle of the pons, which accompanies 

 the pars descendens of the nervus trigeminus. It possesses a characteristic 

 histology and is easily outlined in the medulla, but as it approaches the 

 motor nucleus of the fifth nerve it is cut off by many fibers and is with 

 difficulty delimited without the introduction of the individual element. The 

 nucleus will be described as extending cephalad from the caudal portion of 

 the model. Its relations to neighboring masses of gray matter will be 

 considered. In general, the pars descendens of the fifth nerve lies directly 

 lateral to it. 



At the caudal extremity of the model, the substantia gelatinosa caps 

 the posterior column of the gray matter of this upper cervical cord. It is 

 a convoluted mass and fills the greater part of the column (figures 8 and 9). 

 In modeling, it was necessary to consider it as completely filling the column 

 a thing which it does very soon as one goes cejjhalad (figure 10). At the 

 caudal extremity of the model, then, the substantia gelatinosa practically 

 forms the oval posterior column which lies dorso-lateral to the central canal. 

 It possesses a smooth contour, as shown in figures 1, 2, and 3. The long 

 axis of the oval lies in an oblique plane, the lateral portion being dorsal to 

 the mesial extremity. The column extends slightly cephalad to the superior 

 termination of the decussatio pyramidum in a straight cephalo-caudal direc- 

 tion (figure 2). It widens from below upwards in this portion, as shown 

 in the same figure, a widening to be accoimted for both by the increased 

 size of the substantia and by the rotation of the long axis of the oval in a 

 dorso-ventral direction. This is shown in figure 9, where the long axis of 

 the larger oval has its dorsal extremity somewhat mesial to the ventral. 

 On the dorsal surface there occurs a slight eminence just above the 

 caudal ending of the nucleus fasciculi gracilis, as shown in figure 3. The 

 ventral surface is marked by a somewhat larger eminence in the middle of 

 the decussatio pyramidum (figure 1). As shown in iigure 3, the mesial 

 border extends cephalad and only very slightly laterally until the region 

 of the inferior end of the nucleus fasciculi cuneati is reached. It then is 

 pushed laterally (juite markedly and is overlaid by the projections of the 

 nucleus of Blumenau. The lateral margin of the substantia shows on dorsal 

 view a gradual lateral deflection. 



Figure 2, the lateral view, shows the widened dilatation of the nucleus 

 just cephalic to the superior extremity of the decussation of the pjn-amids. 

 Sui^erior to this, the substantia diminishes slightly in size and shows a 

 gradually increasing tlorsal curving for a considerable distance. Its lateral 



