claustrum

from WordNet (r) 3.0 (2006)

claustrum
    n 1: a layer of grey matter in the brain adjacent to the
         lenticular nucleus

from The Collaborative International Dictionary of English v.0.48

Claustrum \Claus"trum\, n.; pl. {Claustra}. [L., a bolt or bar.]
   (Anat.)
   A thin lamina of gray matter in each cerebral hemisphere of
   the brain of man. -- {Claus"tral}, a.
   [1913 Webster]