How many letters does the top answer for “a bone in the base of the lower jaw of many birds, reptiles, amphibians, and fishes.” have?

The most common answer is articular (9 letters).

Crossword clue: a bone in the base of the lower jaw of many birds, reptiles, amphibians, and fishes.

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

articular 9 letters web-def

relating to or affecting the joints of the body

articulary 10 letters web-def

A bone in the base of the lower jaw of many birds, reptiles, amphibians, and fishes.