72 A Reconstruction of the Niiclear Masses in 



surface is marked by excessive irregularities, as shown in figures 2 and 14. 

 The strilving features of these irregularities lie in the direction of the spurs 

 and in the nuclear connections between the corpus ponto-bulbare and the 

 pontine nuclei, which have already been described. The surface is studded 

 by the spaces filled by the ponto-cerebellar fibers as they leave the pons to 

 course through the brachium pontis to the cerebellum. Between these fiber- 

 bundles numerous nuclear spurs project in a dorso-lateral direction. The 

 character and abundance of these spurs is shown in figure 2; they are most 

 numerous and tyjjical in the middle of the lateral surface, where they are 

 extensive, large, and separated by deep fiber fenestrations. 



As one moves from the lateral to the ventral surface, the surface irregu- 

 larities are seen to change gradually until they assume a fairly typical form 

 on the ventral surface. Here the surface (figure 1) shows short and shallow 

 furrows, deeper sulci, and many ridges more or less extensive. These run 

 in all directions in the upper part, although in the most caudal portion their 

 long axes are in the main transverse. The ventral surface exhibits the ventro- 

 cephalic deflection a))ove noted and two convexities merging in the mid-line 

 in an irregularly delimitetl furrow. The lateral walls of this mid-line depres- 

 sion, as shown in figures 1 and 4, are marked In' bizarre sjuirs and notches. 

 The base of the furrow is marked by irregular corrugations and is wider than 

 its ventral opening. It is filled with transversely coursing fiber-bundles 

 which give rise to marked i)erforations of the lateral nuclear walls. 



On mesial view (figure 4) the mass of nuclei pontis is shown cut along 

 the mid-line. The more cephalic origin of the caudal part of the pontine 

 nuclei, in the mid-line, is well shown. The mesial plate of the arcuate 

 nucleus has become fused with the ventral j^ortion of the ]iontine nuclei, 

 some distance caudal to the point where the pontine nuclei cross the nud- 

 line. The dorso-cei)halic slope of the main dorsal pontine cell-mass is shown 

 extending from the dorsal margin of the mesial plate of the arcuate nucleus. 

 This surface is met, in the middle of its course in the model, liy the dorsal 

 margin of the nuclear material which crosses the mid-line. This dorsal 

 margin of the mid-line gi'ay matter is shown in figure 4, as an irregularly 

 notched and fissured border, witli three chief notches and two caudal pro- 

 jections marring its outline. 



The dorsal surface of the nuclei pontis is not shown in any of the draw- 

 ings, but its outline ai)pears in figure 4. Beginning caudally at a ratiier 

 sharp pole just caudal to the superior termination of the oliva, this dorsal 

 surface, as one progresses cej^halad, widens out dorsally and laterally. It 

 (juickly joins with the mesial and ventral jilates of the arcuate nucleus to 

 siwround the i)yramids. When viewed from the dorsal side, this surface 

 shows two ventral concavities which end in inesial and lateral dorsal i)ro- 

 jections. Tlic hiteral projection forms tlic miclear i)latc of the lateral pontine 

 wall, while the mesial dorsal projection runs along the mid-line to expand 

 info the nucleus I'cticularis tegmenti ])ontis (figures I and It). Between the 



