This chapter describes the topic of the structure and function of the brain, looks at the different parts of the brain, and discusses the membranes which cover the brain—the meninges—and the cerebrospinal fluid which protects the brain and the spinal cord. The brain is a complex organ. Early in its development its cavity becomes divided by constrictures into three parts—forebrain, midbrain and hindbrain. The five main parts of the brain are: cerebrum, cerebellum, midbrain, medulla oblongata and pons Varolii. The cerebrum contains many important nerve centres, which make it not only the largest but also the most highly developed part of the brain. Motor fibres run from the motor centres of the cortex out through the base of the brain into the spinal cord, carrying impulses from the brain. The midbrain consists of two thick stalk-like bands of thick matter which pass out from the base of the cerebrum and run into the pons Varolii.