Final answer:
The inner layer of spongy bone that separates the two outer plates of compact tissue is called trabecular bone.
Step-by-step explanation:
The inner layer of spongy bone that separates the two outer plates of compact tissue in the calvaria and floor is called trabecular bone. Trabecular bone is made up of tiny plates called trabeculae, which form a network of struts that give the bone strength. This type of bone is found in the interior of bones and is lighter and less dense than compact bone.