In developing Amphibia Huxley found a suspensorium of hyoid and mandibular arches similar to the hyomandibular of fish.
"Form and Function" by E. S. (Edward Stuart) Russell
The lower portion of the mandibular arch becomes greatly thickened to support the lower or hinder edge of the mouth.
"Encyclopaedia Britannica, 11th Edition, Volume 14, Slice 3" by Various
By this change in the mandibular arch the mouth becomes narrowed in an antero-posterior direction.
"The Works of Francis Maitland Balfour, Volume 1" by Francis Maitland Balfour