26 A Reconstruction of the Nuclear Masses in 



as it ascends, while the cephalic one-fourth is turned toward the mid-line 

 from the point of the dorsal angle. 



On ventral view, the nucleus of the twelfth nerve shows a gradual 

 increase in its transverse diameter in passing from its caudal to its cephalic 

 pole. The widest portion of the nucleus is attained in the middle of the 

 nucleus of Roller, cephalic to which the lateral wall of the nucleus rapidly 

 curves mesiallj^ to its cephalic i)ole. In the region of the nucleus of Roller, 

 the lateral ventral border is prolonged sharply ventrally for a short distance. 

 The ventral surface of the nucleus is somewhat irregular and slightly curved 

 in its lower two-thirds, with the convexity ventrally. It shows the single 

 ventral bulging and the two dorsal depressions described as occurring in the 

 ventro-mesial border. 



The lateral surface of the twelftli nucleus in its caudal three-fourths is 

 fairly smooth and regular, sloping (as it ascends) slightly laterally from the 

 mid-line and also laterally in its dorsal portion. At the caudal end, the 

 nucleus shows a slight lateral bulging. Above the dorsal angle of the 

 nucleus, the lateral surface sloj^ies in a convexity toward the mid-line to 

 terminate in the cephalic i^ole. The lateral surface really loses its character 

 as the nucleus intercalatus caps the twelfth nucleus, for the dorso-lateral 

 surface here occupies the whole lateral extent of the cell-mass. 



The dorso-lateral surface shows a more marked angle with the lateral 

 surface than does the dorso-mesial with the mesial face. The dorso-lateral 

 aspect of the nucleus is, in general, a flattened straight surface, larger and 

 more striking than the dorso-mesial surface, with a l:)roadened grooving in 

 the caudal one-third, due to the projection of the lateral depression upon 

 it. Slight ventral depressions occur on its surface, corresponding to those 

 seen on the dorso-mesial face. The cephalic one-fourth of this dorso-lateral 

 surface is in intimate contact with the lower end of the nucleus intercalatus. 

 Beginning as a very narrow cap on the dorso-lateral surface of the hypo- 

 glossal nucleus, this nucleus intercalatus covers the remaining cephalic 

 portion of the hypoglossal nucleus, gradually occupying its place as the 

 dorso-lateral border is pushed toward the mid-line. This causes the superior 

 one-fourth of the dorso-lateral surface of the hypoglossal nerve to look 

 laterally, dorsally, and somewhat cei)halad. This ujiper portion of the dorso- 

 lateral face is nuich wider than the other portion of its surface as it assumes 

 also the lateral aspect of the nucleus. 



The caudal pole of the nucleus of the hyi^oglossal nerve shows as a 

 flattened face, pentagonal in outline, wliich lies transversely across the 

 medulla. This is due to the rather abrupt caudal beginning of the nucleus 

 in its characteristic form. The cephalic pole is sharp, lieing formed by the 

 approximation of the various surfaces of the nu('l(>us. 



Many descri])tions of tlie nucleus nervi hypoglossi divide the nucleus 

 into intra-ventricular and extra-ventricular i)ortions. There is no morpho- 

 logical basis for such a division into two approximately equal parts and it 



