The Collaborative International Dictionary of English v.0.48:

Nervation \Ner*va"tion\ (n[~e]r*v[=a]"sh[u^]n), n.
   The arrangement of nerves and veins, especially those of
   leaves; neuration.
   [1913 Webster]

         The outlines of the fronds of ferns, and their
         nervation, are frail characters if employed alone for
         the determination of existing genera.    --J. D.
                                                  Hooker.
   [1913 Webster]