Lamina interna: the ligula.
"Explanation of Terms Used in Entomology" by John. B. Smith
The long sucking "tongue" of bees is probably a modification of the ligula.
"Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4" by Various
A mixture of gold and silver, which was called electrum, was much used for coinage, and I have met with one or two ligulae of this metal.
"Surgical Instruments in Greek and Roman Times" by John Stewart Milne