CHAPTER IX.

THE NERVOUS SYSTEM 148

_Animal and Vegetative Functions--Sensation, Motion, and Volition--The Structure of the Nervous System--The White and Gray Substances--The Brain--Its Convolutions--Cerebellum--The Spinal Cord and its System of Nerves--The Anterior and Posterior Roots--The Sympathetic System of Nerves--The Properties of Nervous Tissue--Excitability of Nervous Tissues--The Functions of the Spinal Nerves and Cord--The Direction of the Fibres of the Cord--Reflex Activity and its Uses--The Functions of the Medulla Oblongata and the Cranial Ganglia--The Reflex Action of the Brain._