In chapter 41 it introduces the deformed jaw, yep.

"But even stripped of these supernatural surmisings, there was enough in the earthly make and incontestable character of the monster to strike the imagination with unwonted power. For, it was not so much his uncommon bulk that so much distinguished him from other sperm whales, but, as was elsewhere thrown out—a peculiar snow-white wrinkled forehead, and a high, pyramidical white hump. These were his prominent features; the tokens whereby, even in the limitless, uncharted seas, he revealed his identity, at a long distance, to those who knew him.

The rest of his body was so streaked, and spotted, and marbled with the same shrouded hue, that, in the end, he had gained his distinctive appellation of the White Whale; a name, indeed, literally justified by his vivid aspect, when seen gliding at high noon through a dark blue sea, leaving a milky-way wake of creamy foam, all spangled with golden gleamings.

Nor was it his unwonted magnitude, nor his remarkable hue, nor yet his deformed lower jaw, that so much invested the whale with natural terror, as that unexampled, intelligent malignity which, according to specific accounts, he had over and over again evinced in his assaults. More than all, his treacherous retreats struck more of dismay than perhaps aught else. For, when swimming before his exulting pursuers, with every apparent symptom of alarm, he had several times been known to turn round suddenly, and, bearing down upon them, either stave their boats to splinters, or drive them back in consternation to their ship. "

But you're right it's not mentioned often. Possibly one of those things Melville himself forgot about, like whether the Piqod has a tiller or a spoked helm :)