Abstract.- Material and Methods.- The Procedure of Classification.- Problems of Terminology and the General Structure of Lacertilian Jaw Musculature.- The Head Musculature of the Gerrhonotinae.- Patterns of Variation within Gerrhonotiform Lizards.- The Head Musculature of the Diploglossinae.- Patterns of Variation within Diploglossine Lizards.- The Head Musculature of the Anguinae.- The Evolution of the M.Intermandibularis Anterior in the Anguidae.- The Phylogeny of the Anguidae based on their Head Musculature.- The Head Musculature of Shinisaurus crocodilurus.- The Head Musculature of Xenosaurus grandis.- The Xenosauridae, a Diphyletic Family?.- The Head Musculature of Anniella pulchra.- The Phylogenetic Position of the Genus Anniella.- The Head Musculature of Heloderma.- Heloderma, a Primitive Platynotan Lizard.- The Head Musculature of Varanus.- Varanus, an Advanced Platynotan.- The Head Musculature of Lanthanotus borneensis.- The Phylogenetic Position of Lanthanotus based on its Head Musculature.- Summary: A Hypothesis to test.- The Skull of Anguinomorph lizards.- The Skull of the Anguidae.- The Skull of the Xenosauridae.- The Skull of the Anniellidae.- The Skull of the Helodermatidae.- The Skull of the Lanthanotidae.- The Skull of the Varanidae.- The Atlas - Axis Complex.- The Phylogenetic Relationships of Lanthanotus: An Inquiry into the Fossil Record.- The Phylogeny and Classification of the Anguinomorpha.- Outlook: The Origin of Snakes.- Acknowledgements.- References.- Abbreviations.- Appendix I.- Appendix II....