The Lower Portion of the Human Brain-Stem. 17 



recedes laterally in a lateral convexity. Dorsal to this extreme mesial edge 

 is a second angle in the nucleus, corresi^onding to the point of attachment of 

 the inferior velum. This line curves around to terminate at the junction 

 of the mesial vestibular nucleus and the nucleus of the fasciculus cuneatus. 

 Lateral to the line of attachment of the velum is a broad, curving, and smooth 

 surface, directly underlying the surface form. This plate is, at its caudal 

 extremity, almost entirely comjiosed of the nucleus fasciculi gracilis, but as 

 it passes cephalad the nucleus fasciculi cuncati gradually encroaches upon 

 it, occupying it entirely at the cephalic limit of the gracile nucleus just below 

 the median vestibular nucleus. This encroachment determines the lateral 

 dorsal termination of the nucleus fasciculi gracilis. 



The mesial view ( Hgure 4) of the nucleus fasciculi gracilis shows the long 

 transverse axis of the nucleus to be dorso-ventral in direction. Caudally, 

 the anterior part of the nucleus does not extend to the so-called central gray 

 matter. The ventral limit of the nucleus soon approaches this gray matter 

 and extends cephalad in a gradual curve to the opening of the fourth ventricle. 

 The mesial surface of the gray matter of the gracile nucleus lies slightly 

 lateral to the central canal and to the dorsal longitudinal fissure (figure 9). 

 It shows slight lateral depressions and projections, corresponding to the 

 curving of the mesial limits as seen on dorsal view. The most marked of 

 these lateral depressions occurs about the level of the sudden widening out 

 of the upper half of the nucleus. The dorsal limit of the nucleus, as seen on 

 mesial view, shows the irregularities due to the dorsal spurs already described. 

 These peculiarities of the nucleus are excellently shown in the mesial view 

 of the model (figure 4). The ventral limit of the nucleus in its uppermost 

 portion follows the line of the tractus solitarius, curving rather ciuickly 

 dorsally, as the nucleus of the tractus becomes associated with the descending 

 vestibular mass. The ventral edge then curves dorsally and caudally to 

 meet the dorsal and cephalic limit of the nucleus. Alesially, then, the gracile 

 nucleus extends in a slight i)rojection cephalad to its dorsal limit, showing 

 medially a triangular projection with the apex cejihalad between the ves- 

 tibular nucleus and the nucleus tractus solitarii. 



The ventral limit of the nucleus fasciculi gracilis is well defined through- 

 out. In the caudal i^ortion the nuclear characteristics permit an easy 

 differentiation from the gray matter about the central canal. In the more 

 cephalic regions the bundles of the fibr arciformes interna? are taken as 

 the mesial and ventral terminations of the nucleus (figure 10). The ventral 

 surface in the caudal parts is almost transverse, but in the more cephalic 

 portions the curve of the internal arcuate fibers forms a curving surface which 

 looks not only ventrally but also laterally. 



The lateral surface of the nucleus fasciculi gracilis is seen in figure 2, 

 which shows the irregular dorsal outline in the lower half, the marked bulging 

 of the upper half, and in part the relations to the cuncatc nucleus. The 

 lateral surface of the lower part of the nucleus really slopes dorsally and 



