84 Journal of Comparative Neurology 



most entirely of longitudinal fibres, is collected in the four re- 

 gions between the horns of the cinerea. These fibrous regions 

 will be designated from their position, the dorsal, ventral 

 and lateral columns, and no attempt will be made to trace the 

 separate tracts ; for, while an individual tract may vary consid- 

 erably in size and direction in its course through the oblongata, 

 the integrity of each column is, on the whole, maintained. In this 

 section (Fig. 8) the metaccele shows as three small openings not 

 connected with either the myeloccele or the dorsal furrow. 

 Figure 9 shows a section a short distance cephalad of that in 

 figure 8. In this the three small diverticles of the metaccele 

 have blended into one cavity, while the metaccele is joined 

 ventrad, by a narrow slit, with the myeloccele ; dorsad the dor- 

 sal furrow widens and the metaccele is roofed in by a narrow tela. 

 Little change is shown in the relative shape and relations of the 

 various parts. The lateral projections of the metaccele become 

 noticeable. A section a short distance cephalad of this (Fig. 

 10) shows the widening of the dorsal furrow and the formation 

 of the broad metaccele. The dorsal cornu of the cinerea is en- 

 croached upon by the dorsal and lateral columns. The dorsal 

 columns take a more horizontal position by the elevation of their 

 mesal borders and project over the metaccele as the ripse, while 

 centrad of this ridge marking the point of union of the convex 

 columns ( as pointed out by Rabl-Ruckard (67 ) ) is a sulcus. 

 Along the mesal portion of the lateral columns small bundles 

 of longitudinal fibres have pierced the cinerea, forming the be- 

 ginning of the reticular area. These reticular areas are formed 

 along all sides of the cinerea, as we proceed cephalad, and 

 seem to be the way in which the longitudinal fibers encroach 

 upon and obliterate the gray areas. Farther cephalad a sec- 

 tion (Fig. 1 1) shows a decided shortening of the ventral cornu 

 with a corresponding progression of the lateral columns ven- 

 tro-mesad. The dorsal column shortens in its lateral diameter 

 and thickens in the dorso-ventral, encroaching upon the dorsal 

 cornu and forming a reticular area in that region. The ventral 

 columns are forced a little dorsad, elevating the floor of the 

 metaccele, making it approximately horizontal. These columns 



