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Medical Definition of Pedunculus cerebri
1. Originally denoting either of the two halves of the midbrain (a relatively narrow "neck" connecting the forebrain to the hindbrain); this term has been variably used to designate only those large bundles of corticofugal fibres forming the crus cerebri, or to designate the crus cerebri plus the midbrain tegmentum; this latter more inclusive usage (crus cerebri and midbrain tegmentum) is preferred; the substantia nigra, while a part of the base of the peduncle (basis pedunculi), is considered a structure separating the midbrain tegmentum from the crus cerebri. See: crus cerebri. Synonym: pedunculus cerebri. (05 Mar 2000)