74 A Reconstruction of the Nuclear Masses in 



The course of the pyramids through the portion of the nuclei pontis 

 included in this model is almost a direct longitudinal one. At the caudal 

 end of the pontine nuclei, the pyramids form a solid column of fibers sur- 

 rounded by the cell-mass of the pons. The cross-section in this area (figure 

 13) shows them to bo almost round. The investing nuclear wall is smooth, 

 marked only by the longitudinal ridge mentioned as occurring on the inner 

 surface of the plates of the arcuate nuclei. As the pyramids are traced 

 cephalad, small spurs project from the including nuclear tissue separating 

 the fibers. Cephalic to these small spurs, occur cell-bridges which divide 

 off a portion of the fibers from the chief bundle of the pyramids. These 

 cell-bridges increase in number and extent, breaking the pyramids up into 

 smaller collections of fibers. Such, then, is the course of the pyramids 

 through the pons, as shown in this reconstruction. This is not given in 

 any of the drawings of the model, but the breaking up of the main Inuulle 

 of the pyramids appears in the cross-section (figure 14). 



NUCLEUS OLIVARIS SUPERIOR. 



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

 nucleus nervi facialis and, sloj^ing dorsally and slightly laterally, terminates 

 ce{)halad in the region of the sensory enlargement of the nervus trigeminus 

 (figure 4). It measures in its longest diameter 9.0 millimeters. It lies along 

 the ventro-mesial surface of the nucleus of the seventh nerve in its extent 

 and then gradually ai)i)roaches the ventral i:>ortion of the mesial surface of 

 the nucleus nervi trigemini. It is mesial to the lateral wall of the pontine 

 nuclei. On its mesial side and ventral side lies the formatio reticularis, in 

 which it occurs; superior to the nucleus of the seventh nerve, it has formatio 

 reticularis also on its dorsal and mesial asj^ects (figure 13). 



The caudal termination of this nucleus olivaris superior is a pointed 

 pole lying in close ai)i)roximation with the ventro-mesial surface of the 

 nucleus of the seventh nerve. It is shown in figure 4, the mesial view of the 

 model. This inferior portion of the nucleus is poorly defined and is sepa- 

 rated with difficulty from the nucleus of the seventh nerve, even though 

 the latter possesses a characteristic histology. The nucleus enlarges into 

 a triangular nuclear mass, out of which three dorso-ventral cell-columns 

 appear clearly defined. These are luiited at their ventral aspect and they 

 spread out from this ventral point as spokes from a hub. Dorsally the ends 

 of these ridges are joined together at a level slightly su])erior to the point of 

 ventral radiation. The two cell-columns which form the nucleus arise from 

 the ventral and dorsal points of union, respectively, and run cephalad, 

 dorsally, and somewhat laterally (figure 13). 



The mesial column arises from the ventral ]ioint of radiation in the 

 caudal cell-collection, as a small continuous ccll-ma-ss. This ((uickly and 

 abrui)tly enlarges into a thin sheet of cells which run cephalad in the charac- 

 teristic direction. This .sheet of cells lies in the general dorso-ventral plane, 



