| formatio | A structure of definite shape or cellular arrangement. Synonym: formation. Origin: L. Fr. Formo, pp. -atus, to form (05 Mar 2000) |
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| formatio reticularis | <anatomy, neurology> A region extending from the pons & medulla oblongata through the mesencephalon, characterised by a diversity of neurons of various sizes and shapes, arranged in different aggregations and enmeshed in a complicated fibre network. (12 Dec 1998) |