The brain is not an entirely solid organ. There are chambers within the brain, referred to as ventricles or, more correctly, cerebral ventricles, to distinguish them from the ventricles of the heart. They represent the remnants of the The central nervous system develops, in the womb, from a strip of tissue, passing along the back of the embryo, and whic... of the developing The brain and spinal cord together make up the central nervous system. Nerves issue from both structures, passing out of..., although they have taken on a much more complex shape than the original embryonic structure. There are four in total, one each side of the midline (referred to as the lateral ventricles) and two more, in the midline, referred to as the third and fourth ventricles, albeit often using Roman numerals.