Diploë

Diploë (/ˈdɪploʊi/ or DIP-lo-ee) is the spongy bone separating the inner and outer layers of the compact bone of the cranium.

In the cranial bones, the layers of compact tissue are familiarly known as the tables of the skull; the outer one is thick and tough; the inner is thin, dense, and brittle, and hence is termed the vitreous table. The intervening cancellous tissue is called the diploë. In certain regions of the skull this becomes absorbed so as to leave spaces filled with liquid between the two tables.