Final answer:
Cranial and facial cells are derived from mesenchyme. Intramembranous ossification forms brain case bones, while endochondral ossification forms the cranial base and facial bones, evolving from a hyaline cartilage model to bone over time.
Step-by-step explanation:
The cranial and facial cells are derived from mesenchyme, an embryonic tissue. During the development of the face and skull, two different ossification processes occur. Intramembranous ossification is responsible for forming the bones in the brain case, where mesenchyme cells differentiate directly into bone-producing cells. In contrast, the cranial base and facial bones are created through endochondral ossification. In this process, the mesenchymal cells first differentiate into cartilage cells and create a hyaline cartilage model of the bone, which eventually grows and converts to bone over a period of years. This conversion process is integral for the growth and the eventual achievement of the skull's full adult size.