Definition, 33; Axial skeleton, 34; Skull, 34; Vertebral column, 39; Cervical vertebræ, 41; Dorsal vertebræ, 42; Lumbar vertebræ, 42; Sacral vertebræ, 43; Caudal vertebræ, 43; Sternum, 44; Ribs, 44; Appendicular skeleton, 46; Anterior limb, 46; Shoulder-girdle, 46; Brachium and Antebrachium, 47; Manus, 48; Carpus, 48; Metacarpus and Phalanges, 49; Posterior limb, 50; Pelvic girdle, 50; Thigh and Leg, 51; Pes, 52. IV. The Digestive System 53 General considerations, 53; Mouth, 54; Salivary glands, 55; Stomach, 57; Intestinal canal, 59; Liver, 60. V. Circulatory, Absorbent, Respiratory, and Urinary Systems 63 Blood, 63; Heart, 63; Lymphatic vessels, 65; Ductless glands, 65; Nostrils, 66; Trachea, 67; Larynx, 67; Diaphragm, 67; Lungs, 68; Air-sacs, 68; Urinary Organs, 69; Bladder, 69. VI. Nervous System and Organs of Sense 69 Brain, 69; Nerves, 71; Sense of touch, 72; Taste and smell, 72; Sight, 72; Hearing, 73. VII. Reproductive Organs 74 Testes, 74; Penis, 74; Ovaries and oviduct, 75; Mammary glands, 75; Secondary sexual characters, 76; Placenta, 76. CHAPTER III ORIGIN AND CLASSIFICATION OF THE MAMMALIA 82 Origin, 82; Classification, 84; Table of orders and families, 88. CHAPTER IV GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION 93 I. Geographical Distribution 93 Zoological regions, 96; Palæarctic region, 97; Ethiopian region, 98; Oriental region, 100; Celebes, 102; Nearctic region, 102; Neotropical region, 103; Aquatic mammals, 104. II. Geological Distribution 107 Sequence of strata, 107; Mesozoic mammals, 109; Multituberculata, 109; Polyprotodont types, 113; Tertiary mammals, 115. CHAPTER V THE SUBCLASS PROTOTHERIA OR ORNITHODELPHIA 117 General characters, 117. _Family_ ORNITHORHYNCHIDÆ, 119; _Ornithorhynchus_, 119. _Family_ ECHIDNIDÆ, 124; _Echidna_, 125; _Proechidna_, 126; Fossil species, 127. CHAPTER VI THE SUBCLASS METATHERIA OR DIDELPHIA 128 General characters, 128; Distribution, 131; Classification, 131. _Suborder_ POLYPROTODONTIA 133