The Lower Portion of the Human Brnin-Steni. 53 



The ventral surface of the nucleus is straight and smooth, excei)t about 

 the sixth nucleus. In this area the nucleus incertus exhibits a dorsal con- 

 cavity with a ventral jirojection along the mesial surface of the nucleus 

 nervi abducentis. This elevation vanishes as the cephalic portion of the 

 sixth nucleus is reached, and cephalic to this the nucleus maintains its 

 smooth and flat form. 



The relative diameters of the transverse and dorso-ventral portions of 

 the nucleus can be made out by comparison of figures 3 and 4. The dorso- 

 ventral diameter, as is shown, is practically constant throughout the extent 

 of the nucleus, while marked difference exists in the transverse. 



NUCLEUS OLIVARIS INFERIOR. 



From the caudal limit at a point in the basilar portion of the medulla 

 5.6 millimeters above the cephalic limit of the decussation of the pyramids, 

 the nucleus olivaris inferior extends cephalad to the joons. The cephalo- 

 caudal diameter of this nuclear mass measures 14 millimeters; the dorso- 

 ventral, 4.3 millimeters; and the transverse, 6.7 millimeters. With the 

 exception of the long cephalo-caudal diameter, the measurements given are 

 those derived by taking the averages of a series of measurements. The 

 transverse axis, if this term be used to designate the locus of the middle 

 points of lines drawn from the dorsal to the ventral surfaces of the olivary 

 leaves, varies in its relation to the antero-posterior ])lane of the raphe. In 

 the lower one-third of the olive this transverse axis forms approximately^ 

 a 90 angle with the raphe. This angle becomes increased in the more 

 cephalic portions of the olive, being about 110 in its middle one-third and 

 reaching in the most cephalic portions an angle of 135 a])proximately (fig- 

 ure 6). With this increase in the angle formed by the transverse axes of the 

 olive with the raphe, the whole olive presents the appearance of having had 

 its cephalic portion rotated laterally while the inferior or caudal end has 

 been held in the transverse, right-angle position. 



The volume of the olive, as determined by the displacement of water 

 by its model with later computation from the volume displaced, is 0.14 cubic 

 centimeter of nuclear material. 



The general form of the inferior olivary nucleus is, as designated b}' 

 Miss Sabin, that of a "hollow shell with a wrinkled wall." This js shown 

 in the separate drawings of the olive (figures 5, 6, and 7) and in the lateral, 

 ventral, and mesial views of the whole model (figures 1, 2, and 4). The 

 nucleus presents for examination dorsal, lateral, ventral, mesial, cephalic, 

 and caudal surfaces. The so-called dorsal surface is actually directed i)os- 

 teriorly only in the lower one-third of the nucleus, for it assumes a marked 

 dorso-lateral deflection in its cephalic jwrtion, with the increased angle which 

 the transverse axis makes with the raphe in this suinn-ior jwrtion. Ihilike 

 the olive in Miss Sabin's reconstruction, the dorsal surface does not pass 



