A single layer of cells that line the ventriclesThe 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 central canal of the developing central nervous system, 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. of the brain and the central canalThe central nervous system develops, in the womb, from a strip of tissue, passing along the back of the embryo, and which then rolls itself into a tube before sinking below the skin surface. This primitive neural tube then develops into the central nervous system, made up of the brain and the spinal cord. In the fully developed adult (i.e. by the age of about 18) the original tubular configuration of the embryonic structure is represented by chambers in the centre of the brain, known as ventricles. In the spine, the tubular structure is all-but obliterated, as the spinal cord develops, being represented by just a narrow tube in the centre of the cord, known as the central canal. of the spinal cordThe main nerve trunk running down the spinal canal and connecting the individual’s mind and consciousness to the rest of his or her body. It is about the size of a person’s little finger, in diameter. It cannot repair itself if damaged..