jawless.

listen to the pronunciation of jawless.
Englisch - Türkisch
çenesiz
Englisch - Englisch
agnathous

Parenthetically, this line treatment suggests an attempt to mimic the agnathous (jawless) head, if we suppose that the jaw area was colored suitably dark in contrast to the face proper.

agnathic

Mortal combat and decapitation are suggested by the eight skillfully and gracefully engraved heads depicted here with their serrated necks, the prominent arrowheads, and the agnathic or jawless head regalia.

having no jaw
{s} lacking a jaw (especially a lower jaw)