The Lower Portion of the Human Brain-Stem. 39 



nerve. From this point upward to the superior termination of the nucleus, 

 the ventricular mesial surface is represented merely by a small mesial ridge, 

 irregularly marked by projection and depression. This ridge occupies the 

 lateral angle of the ventricular floor. Dorsal to this is the cell-mass which 

 lies ventral to the brachium conjunctivum. Ventral to the ridge is a solid 

 cell-mass which continues upward the oblique ventral surface of the medial 

 nucleus. This surface runs cephalad, somewhat irregularly marked by 

 smooth eminences, to end at the general level of cephalic termination of 

 the nucleus. It lies ventral to the caudal spur of the motor cells comprising 

 the main motor nucleus of the fifth nerve. This surface is fairly well sepa- 

 rated from the substantia gelatinosa by a deep groove, crossed by many 

 fiber bundles. 



The lateral surface of this nucleus presents the shape of a triangle, 

 with the base composed of the superior cell-column which accompanies 

 the entering vestibular nerve. The medial side of the triangle is composed 

 of the dorsal edge of the nucleus while the lateral side is the lateral limit of 

 the nuclear material as it gradually recedes from the entering root. Figure 

 2 shows well this triangular shape, placed just cephalad to the ventral 

 cochlear nucleus. The cell-column which projects caudally, laterally, and 

 ventrally from this superior nucleus to the entering nerve is ciuite irregular 

 in form, narrowing at its lateral extremity and widening as it approaches 

 the nucleus. It lies in close relationship to the substantia gelatinosa as it 

 nears the nucleus and forms a lateral wall which soon fuses with the ventral 

 wall of the superior nucleus. As it approaches the cephalic limit, this 

 lateral wall is continued laterally (at the ventral angle of the dorso-lateral 

 face) into a long spur with a dorso-mesial projection (figures 2 and 3). Ven- 

 trally this spur is composed of a fairly large knob-like swelling. Cephalic 

 to this spur a deep fissure runs almost directly transversely, separating the 

 nucleus from that of the fifth nerve (figure 3). As one views this dorsally, 

 the furrow is seen to become much less deep in its mesial extent and the 

 separation at this point is made with considerable difficulty. This dorso- 

 lateral surface of the superior nucleus represents the superior continuation 

 of the vestibular nuclear material which underlies the brachium conjunc- 

 tivum. On dorsal view (figure 3), this portion of the superior nucleus 

 is characterized by a large dorsal projection at its caudal limit on a level 

 with the caudal extremity of the sixth nucleus (figures 4 and 13). Above 

 this smooth eminence, the surface plate enlarges mesially and laterally, 

 with a rotation so that the surfaces face in a dorso-lateral direction. The 

 superior portion of this surface is smooth, but the inferior and lateral parts 

 are marked by irregularities in the shape of small elevations and depressions, 

 with ridges and furrows also apparent. With the exception of a projection 

 at the side of the marked dorsal eminence at the level of the sixth nucleus 

 the mesial edge of this surface is straight, though it shows some slight 

 irregularities. 



