(Chapter 6) Footnote 47:

Approximately two-thirds of the skull comes from primordial membranous cranium (viscerocranium) and one-third from primordial cartilaginous cranium (chondrocranium): occipital (in part), temporalis, sphenoid body and wings, ethmoid, inferior concha, auditory ossicles, and styloid process. The developing brain is covered by membranous bone.