840 MAN 



situated mt'sially, jx)ssesses the large ()\erhan<2;ing lateral extension wliieli is 

 characteristie ol the dorsal niielear aeeiinuilations. This lateral extension ol 

 tlu' nueleus extends outward and almost hides Ironi \ie\\ the more laterally 

 placed nuek'us ol the eolumn ol Burdach. The nueleus ol Coll eontmues 

 upward enelosed by a dwnidlmg mantle ol libers and eontaniin<j; witlim its 

 lateral eonea\it\- a considerable bundle of fibers of the column of Coll. As 

 it approaches the opening of the fourth \entriele it presents a slight lateral 

 deviation produced b\ the widening ol the ventricular system in this locality 

 which has been so characteristic of the beha\ior of these structures in the 

 forms already described. The nucleus does not, ho\\c'\er, participate in the 

 formation of the lateral wall of the lourth \ entricle, l)eing at all times excluded 

 from that cavity by the circumventricular mantle or lining of subepend\ nial 

 gray matter. The nucleus gradually diminishes in size as the ascending libers 

 reach their cells of termination, and it linally disappears at a level only 

 slightly higher than the point ot opening ol the fourth ventricle. In appear- 

 ance the nucleus is more or less solid and is not broken up into any definite 

 arborization by the fibers composing the tract \\ hich lie grouped together in 

 the concax'ity formed by the lateral o\erhang of tiie nucleus. 



Tlu' nucleus of tlu' column of l^urdach appears at a slightly higher h'vel 

 than the ])ri-cedmg nucleus, as a rounded ele\alion on tlu' dorsal surface of 

 the central gra\ maltt'r at about the ]unction ot the body with the lateral 

 horn. It rapidly extends dorsallx', the base wicK'ning whik' its dorsal tt'rmina- 

 tion gradually moves lattaally in con form it \ w it li the de\ lation shown b\ the 

 preceding nucleus. It also develops a lateral o\ (.'rhanging mass of gray matti'r 

 enveloped by a steadily diminishing number of fibt'rs, and m tlu' lateral con- 

 cavity of the overhanging portion ot the nucleus and almost surrounded by 

 it appears a distmet bundle (d tlu' remaining lil)ers of the ascending tract 

 of Burdach. The nucleus continues to increase m size until it reaches the 

 level at which the nucleus of CjoII begins to diminish and then it rather 



