The mandible is composed of several bones as in reptiles.
The operculum of the normal zooecium has become the mandible, while the occlusor muscles have become enormous.
They include the mandible of a mastodon and a portion of a vertebra of a large fish, both found in the Lower Madison Valley; the skull and other parts of a dog (Mesocyon drummondanus), found near Drummond, Granite county; the skull of a Poatrephes paludicola, found near New Chicago,.
This buccal sac is provided with a dorsal mandible and a ventral radula.
Hinds believe that the paired piercers are the inner lobes of the maxillae, and the unpaired piercer the left mandible, the right mandible being absent.