86 Journal of Comparative Neurology 



(Fig. 15). Two large nidi are seen at ni. a, and ni. b, in this 

 section. The position of nidus a shows an apparent connection 

 with the sulcus centrad of it, but the position of nidus b shows 

 no connection with any sulcus whatever. 



Conclusion. — The structure of the metencephal traced 

 cephalad shows only such changes as would naturally result 

 from a change of form from the tubular myel to the widely op- 

 ened oblongata. The dorsal portions first proceed laterad and 

 then ventrad, while the lateral regions move ventrad and mesad, 

 and the ventral columns move dorsad and project as ridges, or 

 lophii, into the cavity of the metaccele. Between these lophii, 

 or projecting fiber tracts, are found the primary sulci formed by 

 the meeting of the convex walls of two fiber tracts. It is also 

 between the fiber tracts that the cinerea is found and observa- 

 tion shows that the form and position of the areas of cinerea 

 depend upon the position of the columns, and as the nidi of 

 the nerves are developed in the cinerea, they seem to have a re- 

 lation to the sulci, but the development of nidi in regions re- 

 mote from the sulci shows that the relation is only incidental. 



Along the mesal line of the floor of the metaccele was 

 found a projecting ridge of neuroglia, (Figs. 10-14). This 

 ridge originates cephalad of the caudal portion of the metaccele 

 and extends cephalad to the region of the 8th nerve where it 

 forms a slight projection into the mesal furrow of that region, 

 (Fig. 14). Through its entire length the endymal cells cover- 

 ing it, are of a slightly modified character. This ridge proba- 

 bly has no morphological significance as it involves only the 

 neuroglia. 



A section of adult myel about 3 cm. caudad of the closing 

 of the metaccele, shows the ventral furrow extending to the 

 ventral commissure of the cinerea. Tracing this furrow cephal- 

 ad we find the raphe beginning to form at the mesal point of 

 the ventral commissure. The raphe gradually increases in 

 length as we pass cephalad, until the region of transition of the 

 cord into the oblongata is reached, where the furrow is reduced 

 to a shallow mesal depression. The most caudal of the same 

 sections shows the almost entire obliteration of the dorsal furrow, 



