INTRODUCTION 1
CLASSIFICATION OF THE MAMMALIA ADOPTED IN THIS BOOK 11
CHAPTER Ⅰ．THE TRANSITION FROM THE REPTILIAN TO THE MOST PRIMITIVE MAMMALIAN TEETH 18
1．The Upper Triassic Mammals Dromatherium and Microcondon 18
2．A new classification of the Mesozoic Mammals 21
3．Illustrations of the chief Triconodonta and Trituberculata 24
4．The origin of the tritubercular type sought in 1888 among the Mesozoic Mammalia 31
CHAPTER Ⅱ．FIRST OUTLINE OF TRITUBERCULAR EVOLUTION IN MAMMALS 36
CHAPTER Ⅲ．TRITUBERCULY IN RELATION TO THE HUMAN MOLAR TEETH AND THE PRIMATES 48
1．Ontogenetic development of the teeth 48
2．＂The history of the cusps of the human molar teeth＂ 55
The concresence theory 57
Mechanical relations of the upper and lower teeth 60
Evidence that the upper human molars were triangular 62
CHAPTER Ⅳ．TRITUBERCULY IN ITS APPLICATION TO THE MOLAR TEETH OF THE UNGULATES OR HOOFED MAMMALS．COMPLETION OF THE NOMENCLATURE 66
1．Disadvantages of previous systems of nomenclature of the molar cusps 66
2．Methods of analysis of molar elements．Nomenclature of the molars of Ungulates 66
3．Application of the theory of trituberculy to the Perissodactyla 72
The horse molar 72
The rhinoceros molar 72
CHAPTER Ⅴ．TRITUBERCULY：A REVIEW DEDICATED TO THE LATE PROFESSOR COPE 74
Polybuny 74
Comparison of nomenclatures 76
Tritubercular homologies 77
The early stages of sexituberculy 80
Lower molars 80
The nomenclature of the molar cusps and crests 82
The evolution of the Ungulate molar 83
CHAPTER Ⅵ．CHRONOLOGICAL OR GEOLOGICAL SUCCESSION OF MOLAR TYPES 91
1．Reptilian Ancestors of Mammals in the Trias 91
2．The Triassic Mammals 94
3．Mammals of the Jurassic 94
4．Upper Cretaceous Mammals 95
5．Basal Eocene Mammals 98
6．Lower Eocene Mammals 98
Résumé of Geological Succession of Types 99
CHAPTER Ⅶ．THE ORIGINAL OR PRIMITIVE STRUCTURE OF THE MOLAR TEETH IN THE DIFFERENT ORDERS OF MAMMALS 100
The major classification of the Mammalia 100
Protodonta 101
Allotheria or Multituberculata 101
Monotremata 105
Marsupialia 108
Molar teeth of Multituberculates，Marsupials(？)，and Placentals in the Upper Cretaceous 115
Insectivora 117
Cheiroptera 129
Carnivora 131
Evolution of carnasial teeth in Creodonta and Fissipedia 135
Convergence of upper carnassials in Creodonta and Fissipedia 138
Fissipedia 142
Rodentia 144
Simplicidentata 145
Duplicidentata 148
Tillodontia 151
Superorder Ungulata 163
Amblypoda 164
Condylarthra 168
Artiodactyla 171
Perissodactyla 174
Chalicotheroidea or Ancylopoda 184
Hyracoidea 185
Proboscidea 186
Sirenia 188
South American Ungulates 189
Cetacea 190
Zeuglodontia 191
CHAPTER Ⅷ．EVOLUTION OF THE PREMOLARS 193
Premolars in primitive Mammals 193
Adaptation of premolars 194
Various upper premolar types 194
Cusp addition in the premolars 195
Superior premolars 195
Inferior premolars 198
CHAPTER Ⅸ．OBJECTIONS AND DIFFICULTIES，AND OTHER THEORIES 201
Ⅰ．That the tritubercular type is not primitive 201
1．The plexodont or progressive simplification theory of Ameghino 201
2．Objections by Fleischmann and Mahn answered by Scott 204
3．The primitive polybuny theory 205
Ⅱ．That the Cope-Osborn theory of the origin of the superior molars in incorrect 208
1．Cusp homologies founded on embryogeny 208
Order of embryonic cusp-development in Insectivora 210
Summary of Woodward＇s conclusion 212
Ontogenetic order according to Marett Tims 213
The premolar analogy theory 215
Palaeontological difficulties in the premolar analogy theory 217
Gidley＇s restudy(1906)of Jurassic-Mammals supports embryogeny and the premolar analogy theory 219
Addendum：the＂trituberculy＂of Zalambdodonts a secondary acquirement or＂pseudo-trituberculy＂ 225
Conclusion 227
CHAPTER Ⅹ．RECTIGRADATIONS IN THE TEETH 229
Homoplasy as a law of latent or potential homology 229
Homology 237
Lankester＇s reply to the preceding article 238
BIBLIOGRAPHY 240