Dewlap

A hound it was, an enormous coal-black hound, but not such a hound as mortal eyes have ever seen. Fire burst from its open mouth, its eyes glowed with a smouldering glare, its muzzle and hackles and dewlap were outlined in flickering flame.

1901 – 1902, Arthur Conan Doyle, The Hound of the Baskervilles Fire burst from its open mouth, its eyes glowed with a smouldering glare, its muzzle and hackles and dewlap were outlined in flickering flame.

He ended up looking at himself in the mirror. His image stared back at him. He was developing a dewlap - a definite dewlap. He waggled under his chin scornfully with his fingers.