Our skulls are protective cavities for our brains.
It's composed of four types of bones: cranial bones, facial bones, ear ossicles and hyoid bone, but two parts are more crucial: the cranium (pl.: craniums/crania) and the mandible.
In humans, these two parts are the neurocranium (braincase) and the viscerocranium (facial skeleton) which includes the mandible as its biggest bone.
The skull forms the anterior-most portion of the skeleton and is a product of cephalisation—housing the brain, and many sensory structures like the eyes, ears, nose, and mouth.
In humans, these sensory parts are part of the facial skeleton.