24 A Reconstruction of the Nuclear Masses in 



limit of the nucleus, but as seen from dorsal view it extends to approximately 

 the same level with the superior end of the nucleus of the sixth nerve. 



In the cephalic portion of the fourth ventricle, just superior to the area 

 of the strisD medullarcs, and lying somewhat lateral to the median line, is 

 the eminentia abducentis (Streeter) formed by the nucleus nervi abducentis 

 and the genu of the nervus facialis. As shown by a comparison of the 

 corresponding areas of the two sides of the reconstruction, the eminence 

 is directly dorsal to the inferior part of the nucleus of the sixth nerve 

 (figure 4). The genu of the seventh nerve is not shown in the model, as only 

 nuclear material was considered. This eminentia abducentis is continued 

 cephalad in a long cephalo-caudal elevation toward the aqueduct of Sylvius. 

 By comparison, this elevation running to the cephalic limit of the model 

 is seen to be overlying the indefinite nucleus incertus in its whole course. 

 Beneath this nucleus, in the cephalic portion, is the nucleus reticularis 

 tegmenti pontis, shown in figure 4, the mesial view. The fovea mediana, 

 having no correspondence to any underlying nuclear structures, is shown 

 between the nucleus incertus on the left and the eminence of the nucleus 

 incertus on the right. Streeter speaks of the overlapping of the sixth nucleus 

 by the nucleus incertus, but does not picture their relationship in his diagram 

 of the floor; a comparison of the findings therefore can not be made, but 

 it is more than likely that the limits are approximately identical. 



The motor portion of the nucleus nervi trigcmini lies slightly caudal 

 and mesial to the cephalic ending of the vestibular nuclear complex in the 

 anterior fovea (fovea trigemini). This coincides with Streeter's diagram of 

 the terminations of the two nuclei. The overlapping of the nucleus incertus 

 by that part of the fiftli nucleus which lies in close relation to the brachia 

 conjunctiva is shown in Streeter's diagram and in the dorsal view of this 

 reconstruction. 



NUCLEUS NERVI HYPOGLOSSI. 



Arising in the central gray matter, on a level with the caudal pole of the 

 nucleus olivaris inferior (figure 10), 5.G millimeters cephalad to the superior 

 limit of the decussatio pyramidum, the nucleus of the hypoglossal nerve 

 extends dorsally and cephalad to terminate about the middle of the nucleus 

 intercalatus. It measures in this adult medulla 11 millimeters in length 

 and averages in transverse diameter about 1.7 millimeters. The measure- 

 ments given by Streeter for the nucleus are 12.3x2.2 millimeters. 



The nucleus lies in its caudal portion ventral to the central canal of 

 the sj)inal cord, close to the mid-line. Its mesial surface maintains through- 

 out intimate relation to the mid-line of the medulla, and the whole nucleus 

 constantly lies ventral to the central canal and the widened fourth ventricle 

 (figure 4). In its lower three-fourths, this hypoglossal nucleus is covered 

 dorsally, and on the dorso-lateral surface by the nucleus aUr cinerea^ (figure 

 10); in the cei)halic one-third, it is capped dorsally and laterally l)y the 



