nervure vs venation

nervure

noun
  • A vein in the wing of an insect. 

  • One of the ribs in a groined vault; a projecting moulding. 

venation

noun
  • The arrangement of veins in a leaf, wing, or similar structure. 

How often have the words nervure and venation occurred in a corpus of books? (source: Google Ngram Viewer )