10 A Reconslrudio?} of the Nuclear Masses in 



the column, becomos ill-defined and irregular in the caudal portion of the 

 decussation, but in its superior })ortion it is accentuated as a laterally 

 projecting tliin sheet of cellular tissue. This curves slightly dorsally, l)ut 

 shows a marked ventral curving in the region just above the pyramids. The 

 shallow depression of the cervical portion of this surface becomes converted 

 into a definite furrow in the caudal half of the decussation; superior to this, 

 it is lacking and the surface ventral to the lateral ridge is smooth. 



Superior to the decussatio pyramidum, the anterior column loses much 

 of its character. Its dorsal surface merges with the cephalo-ventral slope 

 of the formatio reticularis as this latter ]:)ecomes prolonged ventrally in the 

 form of a ground substance fairly free from fiber tracts. This is illustrated by 

 the fusion, in figure 2, of uncolored formatio reticularis with the red motor 

 column. This jDortion of the formatio. with its comparative freedom from 

 fiber tracts and its deeper staining ciualities with carmine, projects laterally 

 just ventrally to the substantia gelatinosa. From this point, it turns sharply 

 ventrally as an irregularly corrugated surface. It merges caudally with the 

 dorsal surface of the anterior column, first as a small bridge of typical tissue, 

 then intermits cephalad, to be connected by a second bridge of gray matter. 

 Sujierior to this second intermission is the continuous connection of formatio 

 with the vanishing anterior column. Coincident with the second bridge of 

 the formatio reticularis occurs a marked lateral projection of the formatit), 

 superior to which is a marked concavity in its surface. The lateral ridge of 

 this surface, which was so prominent in the superior portion of the pyramidal 

 crossing, curves sharply ventrally, cephalad to the i)yramid decussation, and 

 then loses its character on the lateral surface between the two bridges of 

 formatio reticularis. Just caudal to its cephalic termination a division of 

 the anterior column into two parallel masses is suggested from this surface 

 (figure 1). The motor cells are gradually lost in the upper part of this region 

 and as the interior column becomes fused with formatio reticularis the 

 motor cells disa])i:)ear. 



Inspection of the ventral view of the modc^l (figure 1) shows the anterior 

 column on the left pursuing an almost direct cephalo-caudal direction, witli 

 a slight ce])halo-lateral deflection. The anterior column on the right side 

 shows a marked bowing laterally in the region of the decussatio jiyramidum. 

 The left anterior column is broader in the cervical region than in the two 

 superior portions; in its caudal portion the \-entral side is rounder, while 

 in the region of the pyramidal crossing it is flattened and narrowed and 

 al)ruptly marked off from the lateral and mesial surfaces. In the portion 

 cephalic to the superior limit of the decu.ssation the anterior column shows 

 a division into two masses of motor cells. The more mesial of these two 

 columns continues the direction of the primary cohiinn. These two cell- 

 columns are discrete and can be traced cephalad for some distance. The 

 motor cells gradually disai)pear and the two columns merge in that jiart of 

 the formatio, comparatively free from fibers, which projects ventrally. Such 



