Fig. 10. Summary model for the mechanics of venom spitting. The palato-maxillary arch (comprising the pterygoid, palatine, ectopterygoid and maxilla) articulates with the skull at the prefrontal (black rectangle). Immediately adjacent to the palato-maxillary arch is the venom gland and duct; the fang sheath covers the anterior portion of the maxilla and venom duct. The system at rest is shown from a lateral (A) and dorsal (B) perspective. Upon contraction of the M. protractor pterygoideus (PP) the palato-maxillary arch is protracted, rotated in the sagittal plane (C), and rotated in the frontal plane (D). These rotations displace the fang sheath (D,E), removing barriers to venom flow such that when the M. adductor mandibulae externus superficialis (AMES) contracts, venom pressure can expel venom through the specialized exit orifice of the fang (E). P, pressure; F, fang.