68 A Reconstruction of the Nuclear Masses in 



cell-mass of this right arcuate nucleus begins slightly caudally to the left 

 as a rather broad and thin column of cells which decreases in transverse 

 diameter very cjuickly (figiu'es 1 and 10). Reaching a fairly constant trans- 

 verse diameter, the cell-column extends cephalad (figures 11 and 12), with 

 a very marked lateral convexity. It terminates abruptly cephalad on a 

 level below the superior ending of the first portion of the left arcuate. Its 

 superior pole terminates much farther laterally' than on the left. This allows 

 it to approximate the olive more closely as the pyramids decrease laterally 

 in their dorso-ventral diameter. The middle of this first portion of the 

 right arcuate is marked by a deep lateral notch on its mesial surface. 



Cejihalic to this first portion, the curve of the right arcuate nucleus 

 is further continued medially by a small isolated mass of arcuate material, 

 irregularly shaped (figure 1). Superior to this irregular mass, on a level 

 with the division of the left arcuate in two columns, lies the caudal end of 

 the cephalic portion of the right nucleus arciformis. This shows on ventral 

 view (figure 1) as two caudally projecting columns, the mesial being more 

 caudal. This mesial spur is really the ventral border of a mesial plate, 

 similar to that on the other side, which extends from this point to the pontine 

 nuclei. It is quite a thick plate, bordering the deepened anterior longi- 

 tudinal fissure and placed mesially to the pyramid. It shows a number of 

 short dorsal spurs, more numerous and less extensive than those on the left. 

 This mesial plate curves around the pyramids into the ventral plate, at the 

 caudal lateral corner of which is the lateral of the s])urs. Above this spur 

 is a fairly deep, well-differentiated furrow, with a cephalo-caudal direction. 

 The middle of this jjortion shows the same gentle ventral ridge as exhiliited 

 on the opposite side. The lateral margin of this portion of the nucleus is 

 irregular and shows but little lateral deflection until it suddenly widens into 

 the ventral portion of the nuclei pontis. The ventral and mesial jjlates fuse 

 without irregularity into the caudal portion of the j^ontine nuclei. The inner 

 surface (lateral and dorsal) of this curved plate of cells is marked by longi- 

 tudinal fissures and furrows, similar, in all main characters, to those which 

 occur on the left. These ridges are continued upward to mark the course 

 of the pyramids through the nuclcM ]iontis (figure 13). 



The two arcuate nuclei fuse in the mid-line, the connection taking place 

 just dorsal to the anterior longitudinal fissure (figure 1). Both mesial plates 

 send out a rather heavy nuclear column and these merge in the mid-line. 

 The connection, however, ceases before the pons is reached. In the pons, 

 of course, the mid-line connection of the two nuclei can be assumed. 



CORPUS PONTO-BULBARE. 



This bod}'- which Mssick {loc. cit.) .showed to extend from the emergent 

 fifth nerve caudally between the seventh and eighth nerves and to terminate 

 in the lateral wall of the fouiih Ncntricle just caudal to the dorsal nucleus 

 of the cochlear nerve has been modeled in this reconstruction. Only those 



