Agnathic

[…] the heads are inverted and agnathic (lacking a lower jaw) […]

Mouth is without jaws (agnathic) in lampreys and hagfishes and bounded by jaws (gnathic) in all other vertebrates.

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.

[…]an imperforate pharynx which existed in an agnathic lamb.

In the mouth: various irregularities, such as wide separation of the teeth; abnormal development of the canines; the prognathic or agnathic jaw; high arching of the palate; cleft palate—all are found more frequently among persons otherwise degenerate than in normal individuals.

Most pregnancies with agnathic fetuses are associated with polyhydramnios, which probably result from fetal inability to swallow because of persistence of the oropharyngeal membrane.