<Ul> <Li> The cranial cavity is a large, bean - shaped cavity filling most of the upper skull where the brain is located . </Li> <Li> The vertebral cavity is a very narrow, thread - like cavity running from the cranial cavity down the entire length of the spinal cord . </Li> </Ul> <Li> The cranial cavity is a large, bean - shaped cavity filling most of the upper skull where the brain is located . </Li> <Li> The vertebral cavity is a very narrow, thread - like cavity running from the cranial cavity down the entire length of the spinal cord . </Li> <P> Together the cranial cavity and vertebral cavity can be referred to as the dorsal body cavity . In the posterior (dorsal) cavity, the cranial cavity houses the brain, and the spinal cavity (or vertebral cavity) encloses the spinal cord . Just as the brain and spinal cord make up a continuous, uninterrupted structure, the cranial and spinal cavities that house them are also continuous . The brain and spinal cord are protected by the bones of the skull and vertebral column and by cerebrospinal fluid, a colorless fluid produced by the brain, which cushions the brain and spinal cord within the posterior (dorsal) cavity . </P>

Early animal characteristics led to the development of the body cavity in