refers to the pattern of veins or nerves on an organ
• (n.) The arrangement of nerves and veins, especially those of leaves; neuration. • (n.) The arrangement of nerves and veins, especially those of leaves; neuration.
Ner·va'tion noun The arrangement of nerves and veins, especially those of leaves; neuration. « 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. 
refers to the pattern of veins or nerves on an organ