Final answer:
Cranial capacity measures the volume of the interior of the brain case in cubic centimeters (cc), which relates to the size of the brain, not its intelligence or external dimensions.
Step-by-step explanation:
Cranial capacity measures the interior volume of the brain case in cubic centimeters (cc). This is essentially the space available within the skull that would correspond to the approximate size of the brain. It is important to distinguish this from the encephalization quotient (EQ), which factors in body size to deduce the relative size of the brain and is used as an indicator of potential cognitive capabilities within and across species. Moreover, the complexity of the brain is also indicated by the extensive folding in the cerebral cortex, which allows a greater amount of gray matter to fit within the limited space of the cranial cavity. Therefore, the correct answer is D) the interior volume of the brain case in cc.