The Lower Portion of the Human Brain-Stem. 37 



It ends as a thin mass, lying with its long axis dorso-ventrally, lateral to the 

 median vestibular nucleus (figure 3). Its caudal termination is just cephalic 

 to the caudal ending of the nucleus just mentioned. In the first part of 

 its course, the nucleus spinalis is covered dorsally by the nucleus fasciculi 

 cuneati, but as one passes cephalad it soon presents dorsally, as a thin 

 column just lateral to the caudal portion of the median nucleus (figure 3). 

 Its mesial and lateral surfaces in this portion are fairly straight, the mesial 

 well defined, but the lateral poorly differentiated from the nucleus fasciculi 

 cuneati. It spreads out in its ventral portion, so that on cross-section the 

 nucleus shows as a triangle (figures 11 and 12). As the lateral recess opens 

 into the ventricle the median nucleus overlaps dorsally the spinal nucleus, 

 which has gradually displaced laterally the nucleus fasciculi cuneati. Just 

 cephalic to this overlapping, the nucleus spinalis becomes superficial beneath 

 the corpus restiforme, occui^ying the region cephalic to the convex superior 

 end of the nucleus fasciculi cuneati. On cross-section in this area the radix 

 descendens of the nerve lies median to the former, being capped laterally 

 by a dense sheet of nuclear material. Figure 2 shows the nucleus spinalis 

 occupying the whole lateral field dorsal to the substantia gelatinosa. It 

 shows in its lower portion a considerable depression, but soon widens laterally 

 as the dorsal spurs appear on the median nucleus. The lateral border of 

 this surface is at first coincident with the dorsal margin of the substantia 

 gelatinosa, but (as the vestibular nerve enters) this lateral border of the 

 spinal nucleus projects laterally and ventrally to form the apex of a large 

 triangle comprising the whole lateral surface (figure 13). The nuclear 

 material comprising the cell-sheath of the nucleus is composed of a caudal 

 (more mesial) column and a cephalic (more lateral) column (figure 2). 

 Between these the nerve enters the nucleus and separates it from the sub- 

 stantia gelatinosa. The ui^per cell-column slopes caudally, laterally, and 

 ventrally from its origin in the sujierior nucleus; and so the spinal nucleus 

 terminates in the somewhat irregular line of the accompanying cell-columrt 

 as the vestibular nerve enters the brain-stem. These cell-columns about 

 the nerve fuse in jiart at their ventro-lateral terminations with the cells of 

 the corpus ponto-bulbare. Whether the cell-columns shoukl be considered 

 as vestibular or as part of the corpus is not wholly clear, but their histology 

 and position argue strongly for inclusion in the spinal vestibular nucleus, 

 as they hold analogous position to the cells in the radix descendens. Such, 

 then, is the form of the nucleus nervi vestibuli spinalis a small, thin leaf 

 in its caudal portion, widening laterally to its base along the entering vesti- 

 bular fibers. 



NUCLEUS NERVI VESTIBULI LATERALIS. 



With its clearly defined collection of large cells occu])ying the most 

 lateral portion of the main vestibular cell-mass, the nucleus n('r\i vestibuli 

 lateralis exhibits a more or less characteristic form. On the lateial side of 



