RECONSTRUCTION OF TARSIUS SPECTRUM 149 



angles the ventral gray columns and at its dorsolateral angles the connections 

 of the central gray matter with the substantia gelatinosa of Rolando. Con- 

 tinuing upward, the central gray matter retains very much the same position, 

 the connection between it and the ventral gray cokimn being cut across by 

 the decussating fibers of the pyramidal tract. As the dorsal gray columns 

 begin to diverge, the central gray matter migrates dorsally, becoming ilat- 

 tened out, and then gives rise to the dorsal medullary nuclei, while to its 

 ventral aspect is attached the reticular formation. Continuing upward the 

 central gray matter gives rise to the nucleus of the column of Goll, and at a 

 somewhat higher level, to the nucleus of the column of Burdach. As the 

 floor of the fourth ventricle begins to open, the central gray matter comes to 

 the surface and forms the lloor of the fourth ventricle which presents a shal- 

 low depression, concave from side to side and from above downward. The 

 gray matter of the floor of the fcnirth ventricle is spread out in a relatively 

 thin sheet, and presents no particular modeling produced by the underlying 

 structures of the floor of the fourth ventricle. It is continued outward into 

 the lateral recesses and covers the nucleus of Dciters and the triangular 

 nucleus of Schwalbe. It is encroached upon at the angle of the mesial coch- 

 lear nucleus which extends considerably toward the midline. Having passed 

 the level of the lateral recess of the fourth ventricle, the gray matter con- 

 tracts toward the formation of the aqueduct of Sylvius, and the central canal 

 is soon reconstituted by the development of the roof of the fourth ventricle 

 and the lower portion of the aqueduct of Sylvius. It here is in direct relation- 

 ship with the dorsal prolongation of the reticular formation which surrounds 

 it on either side, and receives the superior cerebellar peduncle. Continuing 

 upward, the central gray matter again forms a complete canal which is 

 rather massive and presents walls of considerable thickness. The aqueduct 

 itself is an elongated dorsoventral slit rather than an oval opening, and the 

 central gray matter is continued backward in a long drawn-out projection 



