Ventricles are central cavities in the brain filled with cerebrospinal fluid and are used for protection of the brain. They are continuous with each other and with the central canal of the spinal cord. The two lateral ventricles lie in the cerebral hemispheres and extend across a large area of the brain. The anterior horns of these structures are located in the frontal lobes and are so close together medially that they are separated by only a thin membrane called the septum pellucidum. The ventricles then extend posteriorly into the parietal lobes and their inferior horns are found in the temporal lobes. The third ventricle lies between the two thalamic bodies in the diancephalon. Anteriorly it connects to each lateral ventricle through an interventricular foramen. The massa intermedia passes through it and the hypothalamus forms its floor and part of its lateral walls. The central cavity then becomes thin and tube-like and is called the cerebral aqueduct. It then becomes the fourth ventricle, located in the hindbrain, dorsal to the pons and the superior half of the medulla oblongata. Inferiorly, it connects to the central canal in the inferior medulla and the spinal cord. There are three openings on the wall of the fourth ventricle: a pair of lateral apertures in its side walls and the median aperture in its roof. These apertures connect the ventricles to the subarachnoid space, a fluid-filled space in the meninges that surround the brain and the rest of the central nervous system.

Since nervous tissue is soft and delicate, and since even the slightest pressure can damage the irreplaceable neurons, a considerable amount of protection has been provided for the brain. It is protected by the skull, surrounding membranes called meninges, and by a liquid cushion of cerebrospinal fluid. The meninges are three membranes of connective tissue that lie just external to the brain and spinal chord. Their main functions are to cover and protect the central nervous system (CNS), enclose and protect the blood vessels that supply the CNS, and contain the cerebrospinal fluid. The outermost layer of the meninges is called the dura mater, and is the strongest of the three meninges. It is a leathery sheet of fibrous connective tissue and has two layers. The more superficial periosteal layer is attached to the inside surfaces of the skull bones. The deeper meningeal layer forms the true external covering of the brain. These two layers are fused together except when they separate to enclose the dural sinuses, which are filled with blood. These sinuses act like veins and direct blood from the brain to the large internal jugular veins of the neck. The most relevant of the dural sinuses is the superior sagittal sinus in the superior midline that separates the two hemispheres of the brain. Just deep is the arachnoid mater, which is separated from the dura mater by the subdural space. Deep to the arachnoid mater is the subarachnoid space filled with cerebrospinal fluid where web like threads span to keep the arachnoid mater connected to the pia mater. This space contains the largest blood vessels that supply the brain. The deepest meningeal layer is the delicate, richly vascularized pia mater. This layer clings tightly to the brain surface and follows every irregularity.

Cerebrospinal fluid (CSF) can be found in and around the brain and spinal cord. The CNS literally floats in the CSF. It tends to cushion the brain against trauma, gives buoyancy to the CNS, and reduces its overall weight, while keeping the brain from collapsing under it‘s own weight. The CSF also provides a disposal system by removing waste products from the brain. Cerebrospinal fluid is a clear liquid produced mostly in the choroid plexus attached to the roofs of the four ventricles. CSF forms from blood plasma by filtration from the capillaries of the pia mater. Although cerebrospinal fluid is manufactured in all of the ventricles, it circulates through the system in a specific pattern, moving from the lateral ventricles to the third, and then from the third through the foramen of Munroe to the fourth. From the fourth ventricle, the cerebrospinal fluid passes into the subarachnoid space where it circulates around the outside of the brain and spinal cord and eventually makes its way to the superior sagittal sinus via the arachnoid granulations or arachnoid villi. In the superior sagittal sinus, the cerebrospinal fluid is reabsorbed into the blood stream.

What the ventricles and the meninges have in common is that cerebrospinal fluid is contained and circulates within them continuously. The ventricles and meninges both are capable of manufacturing cerebrospinal fluid. Meninges and ventricles have protection functions as well as processing CSF. Ventricles as well as meninges are continuous from the brain through the entirety of the spinal cord.