Flat bones of the cranium contain a spongy layer called:

1. Compact bone lines it on either side. 2. The middle layer is spongy. 3. Flat bones consist of a layer of diploe, lined on either side by compact bone. 4. So the answer is diploe. _Source: OpenStax 'Anatomy and Physiology 2e', Ch 6 'Bone Tissue and the Skeletal System'_