The internal cranial base (or internal surface of cranial base, latin: basis cranii interna) refers to the inside aspect of the base of the skull.
Anteriorly, the internal cranial base is bounded by parts of the frontal, sphenoid, ethmoid bones; laterally, by the parietal and temporal bones, and posteriorly by the squamous part of the occipital bone. The internal cranial base presents many openings which connect the cranial cavity with other cavities and the outer side of the skull and mostly serve as passageways for blood vessels and nerves.
The internal cranial base accommodates the brain, the intracranial parts of the cranial and spinal nerves, the meninges, intracranial blood vessels, and the cerebrospinal fluid.
Three regions can be distinguished in the internal cranial base known as cranial fossae: the anterior, middle and posterior cranial fossae. Each cranial fossa houses a different part of the brain.