An opening (foramen), in the midline, at the back of the IVth ventricleThe lowest positioned of the four cerebral ventricles. It lies in the posterior fossa but may become partly displaced into the top of the spinal canal in Chiari type 2 malformations., out of which cerebrospinal fluidThis clear, water-like fluid forms, for the most part, within the brain, more specifically inside the ventricles of the brain. Blood flows through structures inside the ventricles, called the choroid plexuses, and clear fluid is produced as a result, passing into the ventricle. This process is akin to blood flowing through the kidneys and urine being produced as a result. An important difference is that, unlike urine, the cerebrospinal fluid is not passed out of the body periodically. Instead, the fluid is re-absorbed back into the blood stream, mostly via the arachnoid granulations, into the cerebral venous sinuses. In the course of a 24-hour period, most healthy adults will produce about 500mls (or a pint) of cerebrospinal fluid, although at... normally flows, as part of its normal circulation around the brain and 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..