The manuscript materials for this book were left in an unfinishedcondition on the sudden death of its author. The earlier chaptershad been in great part arranged in order, but the later descriptivechapters were separate, though notes were found indicating theirprobable sequence. The editors are therefore responsible for the finalarrangement of the latter and have introduced Chapter xv (A Classi-fication of Tetrapoda) in order to show the scheme under which ithas been arranged. We have modified the manuscript by the removalof certain passages which were practically repetitions of passages inother chapters, but we have avoided as far as possible any alterationof either the construction of sentences or the terms used. We are wellaware that certain chapters tend to be incomplete and would almostcertainly have been altered or expanded by the author when revisingthe book as a whole, but we have thought it better to leave themincomplete rather than to attempt to expand them. The only cor-rections we have introduced have been in one or two cases wherea statement has been made directly inconsistent with statementselsewhere.
The division into an earlier, general part and a later, systemic,descriptive part was amply indicated by the author, but the earlierpart of the manuscript, though in order and to some extent dividedup, had not been definitely arranged into chapters. We are thereforeresponsible for this division and for the chapter headings.The aim of the book is to put together the evidence of the variouslines of development of the vertebrae as a guide to the generalmorphological scheme of vertebrate evolution: the problem of theevolution of vertebrae had attracted the author more than fortyyears ago and had remained one of his principal interests throughout.The book is therefore a culmination of investigations and reflectionsof the greater part of an active life devoted to the morphologicalproblems of the vertebrate phylum.
A number of rough sketches were found with the manuscriptillustrating the author's views as set out in the text, but there was no indication of any final selection to be used as illustrations. We havemade use of certain of them which had a sufficient descriptionattached to indicate their probable position. Drawings of these havebeen made by Mrs Gadow, to whom we are also indebted for muchhelp, especially in the composition of the bibliography and index.Fig. 41 has been specially drawn for this book by Dr Bulman. Wehave also freely made use of illustrations which have already beenpublished in the works of various authors and to which reference ismade, more especially in the descriptive chapters. For these ourthanks are due to Dr R. Broom, Dr O. M. B. Bulman, Mrs H. S.Hacker, Professor D. M. S. Watson and Dr W. F. Whittard. Ac-knowledgment is also made to the Akademie der Wissenschaften inWien (Der Fauna der Gaskohle und der Kalksteine der Permformation Böhmens,Fritsch); Messrs Allen & Unwin, Ltd. (Zoology, Sedgwick); TheDirector, American Museum of Natural History, New York (TheBulletin of the American Museum) ; Messrs A. & C. Black, Ltd. (VertebrataCraniata, Goodrich) ; The Carnegie Institution of Washington (Revisionof the Amphibia and Pisces of the Permian of North America, E. C. Case);Herrn W. Engelmann, Leipzig (Festschrift Jür Carl Gegenbaur, Goeppert) ;Herrn Gustav Fischer, Jena (Handbuch der Vergleichenden und Exper.Entwicklungslehre der Wirbeltiere, Schauinsland); Herrn Walter deGruyter & Co., Berlin (Die Stämme der Wirbeltiere, Abel); HarvardUniversity Press (Osteology of the Reptiles, Williston) ; Messrs Longmans,Green & Co. Ltd. (Anatomy, Gray); Messrs Macmillan & Co. Ltd.(Cambridge Natural History, Evans; Structure and Development of Verte-brates, Goodrich; Zoology, Parker and Haswell); The Council of theRoyal Society (Philosophical Transactions); Herrn E. Schweizer-bart'sche Verlagsbuchhandlung (Erwin Nägele), G.m.b.H., Stuttgart(Palaeontographica, von Heune); and to The Council of the ZoologicalSociety of London (Proceedings).

Frontispiece

Editors' Preface

List of Illustrations

PART I GENERAL MORPHOLOGY

I. The Axial Skeleton Its possible external origin 1

II. Segmentation and Resegmentation The formation of metameric vertebrae 6

III. The Composition of the Standard Vertebra Its bilateral origin from four primitive cartilages on each side 9

IV. The Five Ontogenetic and Phylogenetic Stages of the Vertebral Column 16

V. Piiper's Theory The evolution of the vertebral column in Birds 24

VI. Chordacentra and Arcocentra 3o

VII. Further Developments of the Fundamental Scheme 34

VIII. The Vertebral Processes in the Tetrapoda Their definitions, synonyms and distribution 46

IX. Articulation of the Vertebrae The formation of accessory articulating surfaces 55

X. Evolution of an Occipital Joint 65

XI. The Homologies of the Atlas and Second Vertebra of the Amphibia 74

XII.The Nerve Supply of the Musculature of the Tongue Apparatus 85

XIII.The First Three Vertebrae The Proatlas, Atlas and Epistropheus 92

XIV.Ribs 108

PART II SYSTEMIC MORPHOLOGY

XV. A Classification of Tetrapoda 119

XVI. Pseudocentrous Type The Phyllospondylous and Lepospondylous groups 121

XVII. Autocentrous Type Its early origins in the Palaeozoic Amphibia 148

XVIII. Notocentrous Type Its further development in the Anura 164

XIX. The Relationship of Amphibia and Reptilia 172

XX. The Most Primitive Reptiles The Tocosauria of Haeckel 179

XXI. Cotylosauri The primitive Anapsid Theromorpha 196

XXII. Chelonia The most primitive existing Theromorpha 201

XXIII. Pelycosauri The primitive Synapsid Theromorpha 212

XXIV.The Therapsida or Theriodontia More advanced Synapsid Theromorpha which include the Mammal-like Reptiles 221

XXV. Procolophonidae Theronwrph Reptiles of uncertain relationship 228

XXVI. Mammalia 231

XXVII. The Sacro-caudal Region of the Mammalia 244

XXVIII. Primitive Sauromorpha of Uncertain Affinities 257

XXIX.Geckonidae The most primitive surviving Autosauri 267

XXX. Lacertae The Lizards and Chamaeleons 272

XXXI. The Pythonomorpha and Ophidia The extinct and recent Snakes 277

XXXII."Squamata" page The value of the term in classification 289

XXXIII.The Crocodilia and their Permian and Triassic Forerunners 291

XXXIV.Dinosauria and Pterosauria Dominant Mesozoic Reptiles 301

XXXV.Ayes 309

XXXVI.Ichthyosauria and Sauropterygia The Mesozoic marine rovers 326

Bibliography 333

Index 349

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