Which cavity contains the brain and is protected by the skull?

The cranial cavity is the correct answer because it is specifically defined as the space within the skull that houses and protects the brain. The cranial cavity is a vital structure that plays a crucial role in safeguarding the brain from physical injury. The bones of the skull form a rigid protective casing, which is essential for the brain's safety, given its importance in controlling numerous bodily functions and processes.

In contrast, other cavities mentioned serve different functions: the spinal cavity encases the spinal cord, the thoracic cavity is involved with the organs of the chest (such as the heart and lungs), and the pericardial cavity specifically surrounds the heart. Therefore, each of these cavities has distinct roles, highlighting why the cranial cavity is the correct answer in this context.