50 A Reconstruction of the Nuclear Masses in 



diameters are in the main equal, except in its middle portion, where the 

 dorso-ventral diameter exceeds the other. This is coincident with a lateral 

 depression on the mesial face a depression pitted with small holes in the 

 nuclear material. 



From ventral and lateral inspection, the convex lateral border of the 

 nucleus is made out. This margin shows a gentle curving throughout its 

 extent, the convexity of the curve being directed laterally. The greatest 

 lateral deflection of this border occurs at a level corresponding to the angle 

 in the ventral border; cephalic to this deflection the curvature is very gentle. 



NUCLEUS FUNICULI TERETIS. 



Considerable variation in the extent of the nucleus funiculi teretis is 

 found in different human medulUr. While the histological i)icture afforded 

 by this nucleus is similar in all brain-stems, the differences in the cephalo- 

 caudal dimensions and in the transverse diameter in several specimens are 

 marked. Streeter, in his diagram of the relations of the underlying nuclei 

 to the floor of the fourth ventricle, gives the nucleus funiculi teretis as 

 extending from the superior pole of the hypoglossal nucleus to the superior 

 pole of the nucleus intercalatus in other words, occupying as a continuous 

 column of cells the whole of the superior three-fifths of the nucleus inter- 

 calatus. In the adult medulla used for this reconstruction, two distinct 

 and unconnected typical masses of cells are made out as comprising the 

 nucleus funiculi teretis. The caudal mass of cells lies mesial to the cei:)halic 

 portion of the nucleus nervi hypoglossi. It is a very small mass of cells, 

 running through only a few sections, and is not included in this model 

 because of technical difficulties. The larger cell-column has been recon- 

 structed and shows in figures 3 and 4. 



The nucleus lies superficially beneath its eminence on the floor of the 

 fourth ventricle, just lateral to its mid-line. Laterally, it is in relation to the 

 nucleus intercalatus; mesially, to the mid-line of the ventricle (figiu'e 12). 

 Ventrally, it shows an intimate relationshij) to the formatio reticularis. 



As modeled, the nucleus apj^ears as a short column of cells with rounded 

 margins and a larger caudal portion which slopes into the smaller cephalic 

 part. In cross-section, the nucleus shows as a triangle with convex siu'faces 

 and rounded edges (figure 12). When viewed dorsally (figure 3) it exhibits 

 almost a constant trans^'erse diameter throughout its extent with a fairly 

 straight and flat lateral surface and a rounded dorsal face which curves 

 rapidly into the mesial surface, as is seen on cross-section. On mesial view 

 (figure 4), the cephalo-caudal dorsal border is markedly contrasted with the 

 sl()])ing, somewhat irregular v(>nlral line of the nucleus. The caudal border, 

 on mesial view, is wide and turns abru])tly into the ventral margin, wliich 

 slopes irregularly to the tapering upper jiole. This ventral margin shows a 

 slight dorsal notch, cephalic to which the borders run less markedly dorsally. 



