Question

fill in the blank question
four bones of the skull contain paired air spaces called that help to lighten the heavy load of the head.
need help? review these concept resources.

Explanation:

The question is about a specific anatomical structure in the skull. The key information is that these are paired air - spaces in skull bones which lighten the head. The term "sinuses" is well - known in anatomy for such air - filled spaces in bones (e.g., frontal, maxillary, ethmoid, and sphenoid sinuses).

Answer:

sinuses