A STUDY OF THE SUPERIOR OLIVE. 165 



as is characteristic of the more fully developed lateral masses. There was con- 

 siderable variation in the size and form of the lateral portion of this nucleus in the 

 human material examined, though in no case was it entirely absent. Other investi- 

 gators appear to have had similar experiences. Kolliker, whose report is rather 

 confusing in some respects, since it was based entirely upon a study of individual 

 sections rather than upon reconstructions, states that in cross sections of this 

 nucleus one can, as a rule, distinguish three portions more or less distinctly: a larger, 

 medial, more tape-like portion, and two ventral, lateral, more cylindrical forma- 

 tions; yet in man the resemblance to the folded membrane of the larger olive is 

 entirely lacking. Weed, who includes a description of the superior olive in his 

 study of the human brain-stem, says: 



"The nucleus olivaris superior begins just caudally to the middle of the nucleus nervi 

 facialis and, sloping dorsally and slightly laterally, terminates cephalad in the region of the 



sensory enlargement of the nervus trigeminus The nucleus enlarges into a triangular 



nuclear mass, out of which three dorso-ventral cell columns appear clearly defined. These 

 are united at their ventral aspect and they spread out from this ventral point like spokes from 



a hub The mesial column arises from the ventral point of radiation in the caudal 



cell collection as a small continuous cell-mass. This .... enlarges into a thin sheet of 



cells which run cephalad This sheet of cells lies in a general dorso-ventral plane, 



but its ventral border is placed more laterally from the mid-line than its dorsal margin. 

 .... The lateral of the two cell-columns is really double throughout the middle portion 

 of its extent, although it arises singly from the mesial surface of the dorsal union of the 

 three primary radiate columns. Arising from this union, the column extends as a triangu- 

 lar cell-column, placed dorsally and somewhat mesially to the dorsal border of the mesial 



column At this point (the level of the superior .pole of the seventh nucleus) the 



cell-column bends laterally and dorsally across the superior pole of the olive and then 

 pursues a cephalo-lateral course to fuse quickly with its second portion." 



This second portion he describes as arising caudal to the superior pole of the 

 seventh nucleus and ascending, as an elongated oval with the long axis in the dorso- 

 ventral plane, to join the first portion as stated. 



Judging from these statements one must conclude that there is considerable 

 variation in the different specimens examined. One point, however, seems clear; 

 i. e., whatever the condition of the other nuclear parts, this medial portion is always 

 present and well developed, and in comparison with the lateral mass presents a 

 preponderance of the typical spindle-cells. All this tends to confirm the assumption 

 that this portion is the more essential part of the nuclear complex, at least for the 

 proper performance of the functions common to all the types under consideration. 



The medial mass is a large, band-like column of cells which begins caudally 

 just above the ponto-bulbar junction and extends forward to the region of the 

 nervus trigeminus, exceeding the vertical limits of the lateral portion at both poles. 

 It has a decidedly dorso-lateral inclination from below upward and is somewhat 

 twisted upon itself in its long axis. Beginning below as a small oval mass, it speedily 

 enlarges in both lateral and antero-posterior directions and, when fully developed, 

 is semilunar in outline on cross-section, being convex medially and concave laterally, 

 one extremity of the demilune pointing ventro-laterally, the other dorso-laterally, 



