28 A Reconstruction of the Nuclear Masses in 



oblique) averages 1.5 millimeters. Its other dimension is very small, as it 

 is a sheet of three or four cells only in thickness. The nucleus begins below, 

 at the same level approximately^ as does the nucleus alee cinerese. It then 

 extends cei)halad and dorsally, maintaining its close relationship to the con- 

 vexity of the ventro-mesial surface of the nucleus fasciculi gracilis. Roughly, 

 it forms a i)arallelogram with a smooth mesial surface which looks also 

 ventrally. The cephalic border of the parallelogram is not straight, but 

 is curved with a cejihalic convexity. The superior cross diameter is also 

 slightly greater than the corresponding measurement in its caudal portion. 

 From the cephalo-ventral angle of the nucleus projects a well-defined spur 

 which runs ventrally, cephalad, and somewhat laterally. In the middle of 

 its cephalic half the nuclear material is divided into two portions by the 

 central gray matter, but quickly reunites above, the resulting separation 

 giving rise to fenestration of the model of the nucleus at this point. The 

 nuclear mass is histologically very distinct. It is separated from the nucleus 

 fasciculi gracilis by a thin sheath of nerve fibers, while from the nucleus 

 alae cinerese it is segregated by both obliquelj^ coursing fibers and by fibers 

 running in a longitudinal direction. The nucleus stains much more deeply 

 with carmine than does the nucleus alee cinereie. Xo large nerve-cells occur 

 in the cell-mass, but many small cells are found, together with many 

 neuroglia-cells. Few nerve fibrils occur in the nucleus. 



A similarly differentiated nucleus, resembling this just described, is 

 found in the central gray matter, somewhat caudally to the inferior pole of 

 the nucleus nervi hypoglossi. Histologically and pyknoticallj', the two 

 nuclear masses are similar. They bear approximately similar relationships 

 to the central canal, both occurring lateral and dorsal to that structure. 

 No connection between these nuclear masses, placed in the central gray 

 matter, can be made out. On account of technical difficulties this lower cell- 

 mass was not modeled, but, as far as can be stated from the results of study 

 of serial sections, the lower mass also forms a somewhat similar sheet of cells, 

 but possesses greater thickness than does the upper collection. 



The significance of these two cell-sheets is not known. There apparently 

 exists a very close relationship to the nucleus ake cincreae, especially in thi' 

 more cephalic mass. 



Jacobsohn (1909) has described, under the term ''Nucleus sympathicus 

 nervi vagi," a cell-collection which coincides in part with the more cephalic 

 of the two nuclei under consideration and in part with the nucleus ake cinerene 

 as here modeled. His upper limit to the nuclear material is placed at a 

 much highei- level than found in this model. ( 'ajal has included similar cell- 

 collections in the dorso-mesial nucleus of the tractus solitarius. 



The nucleus ake cinereie may be roughly described as an irregularly 

 shaped, curving nucleus, with dorsal convexity, wliicli begins caudally as a 

 thin sheet of cells widening out in its middle portion and exhibiting an 

 irregular triangle on cross-section in its uppcn- jjortion. l^ecause of its marked 



