We just learned about the Frenulum of the Lower Lip.
Another part of the mouth is the Labial Commissure of the Mouth.
This is a big long name that really just means the corner of your mouth where your upper and lower lips meet.
The word labial means lips, and commissure means joining.
(from: wikipedia - labial commissure of mouth)
Kid Facts - Blast from the past: Maxillary Second Molar
