The Lower Puiiion of Ihv IIuiikdi Brain-Stem. 25 



nucleus intercalatus. Lateral to the nucleus, throughout its extent, the 

 nucleus of the tractus solitarius occurs, ^'ontral to it, are the formatio 

 reticularis and the fasciculus longitudinalis dorsalis, with also the nucleus 

 of Roller in its cephalic one-third (figures 4 and 11). 



Miss 1^'abin did not model the hypoglossal nucleus accurately, because 

 of technical difficulties, but merely rei)resented its position in her recon- 

 struction, i^he states that the nucleus corresponds in length, however, to 

 the nucleus olivaris inferior. In this reconstruction of the adult medulla, 

 it is seen that the nucleus of the hypoglossal nerve corresponds merely to 

 the caudal three-fifths of the inferior olive. The hypoglossal and inter- 

 calated nuclei, on the other hand, together corresi)ond to the cephalo-caudal 

 extent of the inferior oli\ary nucleus. 



The nucleus nervi hypoglossi may be described as an elongated column 

 of cells, pentagonal in cross-section, gradually increasing in size from its 

 caudal extremity to its dorsal angle at the eminentia hypoglossi and then 

 rapidly tapering to its cei:)halic pole (figure 4). It presents for examination 

 (in addition to its caudal and cephalic poles) five surfaces mesial, lateral, 

 ventral, dorso-mesial, and dorso-lateral. The characteristics of the nuclear 

 form are shown in large part in figure 4, a mesial view. The dorsal border 

 shows a marked dorsal angle at the junction of the cephalic one-fourth 

 with the caudal three-fourths. Above this, the border curves ventrally to 

 terminate just anteriorly to the nucleus intercalatus, in a rather sharp pole. 

 Caudally from this angle, the dorsal border slopes in a fairly straight line 

 caudally and ventrally; this border shows several depressions with curving 

 limits. In the caudal part the dorsal border dips into a rather deep ventral 

 depression, then projects directly caudally for a short distance, to turn 

 sharply ventrally, forming the inferior pole. The ventral border, from mesial 

 view, shows a gradual ventral bulging in its middle portion, sloping gradually 

 into a shallow dorsal depression cephalad and into a more abrupt dorsal 

 concavity caudally. In this cephalic depression lies the small nucleus of 

 Roller. The mesial surface lying along the raphe is smooth, but the dorso- 

 mesial surface, into which the mesial surface slopes, shows gradual irregu- 

 larities due to the ventral depressions noted as occurring on the dorsal 

 border. In the most caudal and cephalic portions tlie mesial and tlorso- 

 mesial surfaces are fused into one gradual convexit.y. 



From dorsal view (figure 3), the dorso-mesial siufaee alone is seen. 

 Arising as it does just caudally to the nucleus ahe cinereie, this nucleus 

 obscures the dorso-lateral surface in its lower three-fourths (figure 10) while 

 the cephalic one-fourth of the nucleus of the twelfth nerve is covered by the 

 nucleus intercalatus, which forms a well-defined dorso-lateral cap, closely 

 adhering to the cephalic dorso-lateral surface. The elevation between the 

 dorso-mesial and dorso-lateral faces of this hypoglossal nucleus is comi)osed 

 of two portions, both of which are fairly straight. The caudal three-fourths, 

 that portion below the dorsal angle, slopes slightly away from the mid-line 



