CHAPTER IV. THE ORGANS OF SPECIAL SENSE 57 The Nose, 57--The Sense of Smell, 58--The Mouth, 59--The Hyoid Bone, 60--The Teeth, 60--The Sense of Taste, 61--Salivary Glands, 61--The Tonsils, 62--The Ear, 63--Eustachian Tubes, 63--Sensation of Hearing, 65--The Eye, 66--Lachrymal Gland, 68--Coats of the Eye, 68--Light Rays and Sight, 70--Accommodation, 72--Color Perception, 73. CHAPTER V. THE NERVOUS SYSTEM 75 The Cerebrum, 75--The Cerebellum, 78--Pons Variolii, 78--Medulla Oblongata, 78--Spinal Cord, 79--Brain-centers, 81--Motor Tract, 82--Sensory Tract, 82--Reflex Action, 83--Cranial Nerves, 83--Spinal Nerves, 84--Brachial Plexus, 85--Sacral Plexus, 85--The Sympathetic System, 87--The Sympathetic Nerves, 87. CHAPTER VI. THE BACK 88 The Spine, 88--The Vertebræ, 88--Muscles of the Neck, 92--Muscles of the Back, 93. CHAPTER VII. THE CHEST 96 The Sternum, 97--The Ribs, 97--Costal Cartilages, 98--Muscles of the Chest, 98--Diaphragm, 98--Mammary Glands, 100. CHAPTER VIII. THE HEART AND CIRCULATION 101 The Heart, 101--The Pericardium, 101--Cavities of the Heart, 103--The Endocardium, 103--The Valves of the Heart, 103--Circulation, 105--Circulation in the Fetus, 106--Arteries, 107--Veins, 109--Portal Circulation, 109--Pulmonary Circulation, 110--Nerves of the Heart, 110--Heart Sounds, 111--The Heart Beat, 111--Factors Affecting Circulation, 112--The Pulse, 113--Blood Pressure, 114--Nerve Supply of the Blood-vessels, 115--The Blood, 116--Composition of the Blood, 116--Coagulability of the Blood, 117--Blood-corpuscles, 118. CHAPTER IX. THE LUNGS AND RESPIRATION 121 The Larynx, 121--The Trachea, 123--The Thyroid Gland, 124--The Thymus Gland, 124--The Bronchi, 125--The Lungs, 125--The Pleura, 125--The Mediastinum, 126--Respiration, 127--Air, 129--Respiratory Sounds, 129--Changes in Air in Lungs, 129--Effect of Respiration on Blood, 130--Nervous Mechanism of Respiration, 130--Variations in Respiration, 131.