Fig. 2. Cranium and lower jaw of Bufo showing the mouth-opening muscle (depressor mandibulae=DM) and the largest of the mouth-closing muscles (levator mandibulae posterior longus=LM). The jaw joint is indicated by a white circle, and the in- and out-levers are indicated by white bars. Contraction of the depressor mandibulae (upward arrow) produces rotation of the lower jaw about the joint (downward arrow).