The Lower Portion of the Human Brain-Stem. 41 



inspected from the ventral surface, while from mesial view it shows as a 

 shar]:) anp;le due to the great ventral concavity and slight dorsal convexity 

 causing it. The caudal jiole is placed dorsally and laterally to the mid-axis of 

 the nucleus. It is formed by the surfaces approximating in gentle convexi- 

 ties l)clow the margin of dorsal and mesial projection. It is a rounded 

 extremity, lying in close relation to the mesial vestiliular nucleus. When 

 viewed mesially (figure 4) the dorsal border of the nucleus forms a fairly 

 straight line, somewhat notched by the lower extremity of the nucleus 

 intercalatus. The ventral surface shows a marked convexity and bulging 

 in its caudal portion, the cephalic portion remaining comparatively straight 

 until the final concavity is begun. 



All of the surfaces of the nucleus are, in genei'al, rounded so that there 

 are no margins between these faces. The irregularities and characteristics 

 of the oval nuclear mass have already been pointed out and need no further 

 description. The factors which seem to play the greatest part in modif\'ing 

 the true oval character of the nucleus are the superior portion of the luicleus 

 intercalatus and the peculiar looping of the seventh nerve. 



NUCLEUS NERVI FACIALIS. 



The nucleus of the facial nerve, lying in the lateral de])ths of the formatio 

 reticularis at about the level of the caudal end of the nuclei pontis, is shown 

 in the mesial view of the model (figure 4). It also appears on cross-section 

 in figure 13. The caudal end of the nucleus lies on a level with the most 

 cephalic portion of the nucleus ambiguus. The cephalic pole of this nucleus 

 corresponds in position to the similar jiole of the nucleus ncrvi abducentis. 

 In its cephalo-caudal diameter tlie nucleus measures 4.7 millimeters; in its 

 greatest transverse diameter, 2.8 millimeters; and in its greatest dorso- 

 ventral diameter, 4.1 millimeters. 



The relations of the nucleus to other nuclear masses vary in the several 

 portions of the nucleus. The substantia gelatinosa lies dorso-lateral to this 

 nucleus nervi facialis (figure 13). Lateral and somewhat ventral to its 

 caudal half is found the scattered nuclear material comjjrising the corpus 

 ponto-bulbare. Ventro-mesial to its cei)halic two-thirds lies the nucleus 

 olivaris superior, in very close relationshij) throughout. The other relations 

 of the nucleus are wholly concerned with the formatio reticularis. 



Essick (1912) has described the nucleus of the facial nerve as being 

 a pear-shaped cell-mass. With his description of the nucleus in the embryo, 

 this reconstruction of the adult nucleus agrees. In general, the nucleus 

 may be said to be a rounded mass which tapers gradually c(>phalatl after 

 a sudden constriction in its transverse and antero-posterior diameters (fig- 

 ure 4). Beginning caudally in a rather shar]) pole, the nucleus increases very 

 rapidly in all diameters, but especially in the dorso-mesial direction. This 

 more rapid increase in the oblique diameter cau.ses the luicleus to assume 

 an approximately oval shape soon after its caudal origin. The surfaces arc 



