Wikipedia
Simian shelf
The simian shelf is a bony thickening on the front of the ape mandible. Its function is to reinforce the jaw, though it also has the effect of considerably reducing the movement of the tongue by restricting the area available for muscles.
Humans are the only primates to have protruding chins, though some fossils of early humans show evidence of a simian shelf.
Usage examples of "simian shelf".
Elliot made additional measurements of the molar cusps, the jaw, the simian shelf, and the brain case.