Chapter 15FIG 1 Figure 15.1 The unique dual jaw-closing mechanism present in all four major clades of caecilians consists of the mechanism ancestral in vertebrates, the masseter adductor mandibulae, a muscle that pulls up on the lower jaw, and a new mechanism, the masseter interhyoideus posterior, which pulls down on the processus retroarticularis (pret) an extension of the dentary bone. The result is that the lower jaw swings up. This mechanism is progressively more developed in more derived caecilian clades. Redrawn from Nussbaum, 1983. Chapter 15FIG 2 Figure 15.2 A cladogram depicting relationships among the families of extant caecilians. Based on Wilkinson and Nussbaum, 2006. Chapter 15FIG 3 Figure 15.3 Geographic distribution of the extant Caeciliidae. Chapter 15FIG 4 Figure 15.4 Representative caecilians. Clockwise from upper left: Sao Tome caecilian Schistometopum thomense, Caeciliidae (R. A. Nussbaum); monarch tailed caecilian Ichthyophis monarchus, Ichthyophiidae (L. L. Grismer); Bannan caecilian Ichthyophis bannanicus, Rhinatrematidae (E. D. Brodie, Jr.); African buried-eyed caecilian Scolecomorphus vittatus, Scolecomorphidae (L. W. Porras). Chapter 15FIG 5 Figure 15.5 Geographic distributions of the extant Ichthyophiidae and Rhinatrematidae. Chapter 15FIG 6 Figure 15.6 Geographic distributions of the extant Typhlonectidae, Scolecomorphidae, and Uraeotyphlidae. Chapter 15FIG 7 Figure 15.7 Representative caecilians. From left: Water caecilian Typhlonectes natans, Typhlonectidae ( C. Schwalbe ); Kannan caecilian Uraeotyphlus cf. narayana, Uraeotyphlidae (D. J. Gower, The Natural History Museum, London).