12 A Reconstruction of the Nuclear Masses in 



this fusion is not well shown in the model because of the fact that the formatio 

 reticularis is surroniidefl by the nuclei which separate the formatio from the 

 fiber tracts which bound the brain-stem in tliis j^ortion. The central gray 

 matter of the cord will here be describeah as it goes cephalad to merge with 

 the medullary formatio reticularis, and the extreme mass of gray matter of 

 the cord will hv briefly commented upon. 



The ty])ical cross-section of the central gray matter of the upper cervical 

 cord is shown in hgure 8. Here it can be seen to consist of a central body, 

 surrounding the central canal, and of two arms on each side projecting 

 from the ventral and dorsal angles of the lateral surface. Dorsally, the arm 

 is long and curving (eg in figure 3), constituting the posterior column with 

 its substantia gelatinosa. In the mid-line this arm is elevated into a very 

 slight dorsal ridge. The lateral surface of the central gray matter shows a 

 concavity extending upward into the decussatio pyramidum; this concave 

 sui-face results from the curve of the j^osterior arms of the central gray matter 

 and the mesial i)rojection of the anterior columns. The floor of this depres- 

 sion is very smooth except near its ventral termination in the anterior column; 

 here the surface is raised into a definite lateral ridge. Ventral to this ridge, 

 the surface slopes rapidly into the dorsal surface of the anterior column. 

 Anteriorly the body is characterized by a slight mid-lino ventral ridge, on 

 each side of whicli are concave surfaces. 



The central gray matter is considerably affected by the decussatio 

 pyramidum. The most striking of these changes consists in the breaking 

 up of tlie anterior arm of the gray matter by tlie obli(iuely coursing jiyram- 

 idal fibers (figure 9). On the left side of the model, as shown in various 

 figures, the reconstruction was limited to the solid mass of the anterior 

 column and to the undisturbed portion of the central gray matter. Inspec- 

 tion of figures 2 and 4 shows well the resulting mori)hological changes in the 

 central gray matter. The ventral border is turned dorsally in a gradual 

 convexity, l)ut with a more rapid dorsal deflection than the central canal 

 exhibits (figure 4). This figure also records the marked irregular projections 

 of the ventral border. The lateral surface of this central gray matter shows in 

 its ventral jioi'tion no lateral curving because of the separation of the anterior 

 column, but the dorsal con\exity is continued to the ventral margin in tlie 

 mid-line. This ventro-Iateral surface which results is marked by many 

 irregular projections, most of them sliort and tliick. At a point opposite 

 the caudal end of the nucleus fasciculi gracilis (figure 2), the central gray 

 matter shows its first merging into formatio reticularis, for here it is that 

 the peculiar filier-free ])()rtion of the formatio l^egins to project ventro- 

 laterally to connect finally- with the anterior colunm. This mass is separated 

 from the substantia gelatinosa by a very deep and narrow fissure which 

 ciu-ves inwardly, foHowiug the ventral curve of tlie substantia gelatinosa 

 (figures 1 and 2). .McsiaUy, tliese i)rojections are separated from the ventral 

 l)r()jection of the cciilral gray matter by a deep, and soinewhal wide, irregular 



