maxilla vs underjaw

maxilla

noun
  • Either of the two bones that lie with one on each side of the upper jaw lateral to the premaxilla and that in higher vertebrates bear most of the teeth. 

  • An upper jaw especially of humans and other mammals in which the bony elements are closely fused. 

  • One of the first or second pair of mouthparts posterior to the mandibles in many arthropods that are used for tasting and manipulating food. 

underjaw

noun
  • the lower part of the jaw 

How often have the words maxilla and underjaw occurred in a corpus of books? (source: Google Ngram Viewer )