The Lower Poiilon of the Human Brain-Stcni. 51 



This gives rise to the broadened caudal half of the nucleus and a smaller 

 tapering superior portion. The upper pole is rounded and small. The 

 surfaces of the nucleus are all fairly smooth and regularly sloping into each 

 other. The ventral surface shows an irregularity coincident with the dorsal 

 angle in the ventral margin. It is flatter and less rounded than the mesial 

 and dorsal surfaces. 



NUCLEUS LATERALIS. 



Inserted in the formatio reticularis of the medulla between the sub- 

 stantia gelatinosa of the nervus trigeminus and the inferior olivary nucleus 

 is the column of cells known as the nucleus lateralis (figure 11). Beginning 

 caudally at the level of the third dorsal transverse sulcus of the olive (a 

 point midway between the inferior end of the dorsal accessory olive and the 

 caudal pole of the inferior olivary bod}') , this lateral nucleus extends cephalad 

 to the superior limit of the dorsal accessory olive. Dorsal to the nucleus 

 is the substantia gelatinosa; ventral to it is the dorsal leaf of the olive. Its 

 mesial edge is parallel in part to the lateral border of the dorsal olive. 

 Laterally the nucleus is in relation to the corpus restiforme. 



These, then, are the relations of this nucleus lateralis to the other 

 nuclear masses about it in the medulla. The mori:)hology of this nucleus, 

 as reconstructed from the adult medulla, concerns a distinct and continuous 

 column of cells, well differentiated from the formatio reticularis in whose 

 lateral and ventral angle it lies (figures 2 and 4). At its caudal end the 

 nucleus is small, but as it continues cephalad a gradual increase in size 

 occurs, the nucleus reaching its maximum about the level of the middle of 

 the dorsal accessory olive. Just below this level the nucleus sends out a 

 distinct lateral spur which curves slightly ventrally to conform to the curva- 

 ture of the olive. While in the main the nucleus maintains a fairly straight 

 course, it does show slight deflections from its main axis. One such deviation 

 occurs just abo^c its caudal end, the axis here turning ventrall}' after a short 

 dorsal ascent. Five processes project angularly to the dorsal side from the 

 main column of the nucleus, the most cephalic of these occurring just below 

 the cephalic end of the cell-column, two occurring in the area of greatest 

 cross-section, the other two being more caudally situated. Just caudal to 

 the cephalic end is a prominent ventral spur, below which the nucleus widens 

 after taking a slight curving direction, the convexity being dorsal. In the 

 part of greatest cross area, the lateral surface is marked by deep notches. 

 From the main cell-mass, several mesial projections occur; these have prac- 

 tically all a slight dorsal deflection. Two of these, in the caudal one- third 

 of the nucleus, are especially well marked. 



In the lower half of the nucleus the transverse and dorso-ventral 

 diameters are about equal, but in the cephalic jiortion of this nuclear column 

 the antero-posterior diameter is in excess of the transverse. The conflgiu'a- 

 tions of the nucleus are wellshown in figure 2, 



