Structural correlates of tarsal and metatarsal functioning in Iguana (Lacertilia; Iguanidae) and other lizards

Abstract

In lizards, the metatarsus is laterally directed at the time of pedal plantarflexion. During pedal plantarflexion, the metatarsus undergoes an initial rotation around its long axis followed by an extension of the ankle joint. The mesotarsal joint guides the metatarsus during the transition from rotation of the metatarsus to extension of the ankle joint. The proportions of the metatarsus are related to the lateral orientation of the metatarsus. The fifth metatarsal functions as a lever in two different ways during pedal plantarflexion: during rotation of the metatarsus, it increases the leverage of the pedal flexors by placing the line of action of these muscles lateral to the mesotarsal joint; during extension of the ankle joint it increases the leverage of the pedal flexors by placing their line of action ventral to the intratarsal joint. The transverse metatarsal arch acts as a counterbend during rotation of the metatarsus. Movement at the fifth metatarsal – fourth distal tarsal joint does not contribute to movement of the fifth digit during grasping, although the fifth metatarsal plays a passive role in grasping by acting as a pulley around which certain tendons pass.