The Lower Portion of the Human Brain-Stem. 69 



parts, however, which contained sufficient nuclear material to justify model- 

 ing have been includetl. As one passes from the spinal cord cephalad in 

 series, the corpus is first met in the lateral wall of the ventricle just dorsal 

 to the caudal half of the medial vestibular nucleus. This most caudal 

 portion of the corpus is shown in the I'econstruction as an oval of nuclear 

 tissue on the dorsal surface of the middle of the caudal half of the medial 

 vestibular nucleus (figures 2 and 3). Traced from this i)oint cephalad, the 

 corpus for a short distance loses most of its nerve-cells. As the amount of 

 nuclear material is not sufficient to justify modeling, no connection is shown 

 in the model between this most caudal oval and the more cephalic portions. 

 The tract next becomes sufficiently endowed with nuclear material in the 

 region just caudal to the most inferior portion of the dorsal cochlear nucleus. 

 Here it is represented (figures 1, 2, and 3) by a thin sheet of cells, lying caudal 

 and mesial to the dorsal cochlear nucleus. It is curved by the corpus 

 restiforme upon which it lies. Its cephalic border is prolonged ventrall}^, 

 mesially to the dorsal cochlear nucleus. An abrupt termination has been 

 given to the cori)us at this point by the ending of the sections in the block 

 of tissue used as a unit for embedding. It is met, however, as soon as the 

 correction for loss in the blocks is made, lying mesial to the caudal extremity 

 of the ventral coclilear nucleus in the same dorso-\entral plate. This is 

 shown in figure 3. From this point, the corpus ponto-l)ulbare is represented 

 by a continuous cell-mass stretching to the nuclei pontis. Beginning here, 

 mesial to the caudal limit of the ventral cochlear nucleus, the corpus forms 

 at first a widening mass of cells with the long axis transverse (figures 1, 3, 

 12, and 13). Shortly after its origin, it spreads transversely toward the 

 mid-line in an irregular arm of nuclear tissue which stretches mesially anil 

 somewhat dorsally toward the substantia gelatinosa and the nucleus of the 

 seventh nerve. Two small cell-masses occur ventral to this arm (figur(> 1). 

 The main cell-column of the corpus passes cephalad, \entrally, and slightly 

 laterally, following the line of the ventral cochlear nucleus. It broadens 

 somewhat at the cephalic limit of this nucleus and gives origin to two mesially 

 and dorsally projecting arms, one of which fuses with the cell-column from 

 the s])inal nucleus of the vestibular nerve and the other with the colunm 

 from the superior nucleus, as these two columns meet the entering vestibular 

 nerve. These two projecting arms from the corpus ponto-bulbare are 

 marked by great irregularities by spurs projecting in every direction, by 

 sudden increases and decreases in diameters, and by small isolated cell- 

 masses occurring along the course of the nerves. The cephalic end of the 

 mesial of these two arms comes into contact with tlie substantia gelatinosa. 

 The main cell-mass of the corpus, decreased in size after the projection of 

 these two arms, continues cei)halad beyond the cephalic pole of the ventral 

 cochlear nucleus. This is shown in figures 1, 2, and 3. A thinner mesial 

 column of cells accompanies the main mass (figure 1, csjiecially). The main 

 mass and the smaller mesial colunm extend cephalad witli a slight \-entral 



