Nails, 42 Uses of the, 44 Nasal cavities, 192 duct, 201 Nerve, Auditory, 222 Glossopharyngeal, 189 Gustatory, 189 Olfactory, 193 Optic, 197 Sympathetic, 158 Nerve cells, 150, 159 Nerve fibres, 149 Nerves, Cranial, 154 Spinal, 156 Functions of the, 160 Sensory, functions of the, 160 Motor, functions of the, 160 Sympathetic system of, 158 Nervous system, 148, 149 Cerebro-spinal, 150 Nervous tissue, Properties of, 159 Nose, 192 Nutrition, Processes of, 80 O. Oesophagus, 90 Oil, Sources of, in food, 59 Old-sight, 215 Olfactory nerve, 193 Optic nerve, 197 Orbicular bone, 220 Orbit of the eye, 199 Organic substances as food, 57-62 Organs of circulation, 107 Digestion, 81-91 Respiration, 123 Sight, 198 Voice, 228 Oxygen, 131 Amount of, consumed in respiration, 132 Continually supplied to the atmosphere, 141 P.