Underjaw n. : The lower jaw.

Example:


Taxonomy
lips, faults, Sheltie, muzzle, lower lip, upper lips, skull, minor faults, mouth, flews, underjaw, dog, Notebook, skin, jawbones, teeth, illustrations, lip fit.

Defination from the web:
underjaw look deeper than it usually does to us from our superior height. ... I have drawn what I consider to be a middle-of-the-road muzzle and underjaw on which to demonstrate these lip faults. ...