Final answer:
The fetal face is relatively small compared to its cranium, which is more proportional at birth. As development progresses, the facial features grow substantially, particularly during early childhood. In adulthood, the cranial and facial bones fuse, creating the mature skull structure.
Step-by-step explanation:
The size of the fetal face in comparison to its cranium is significantly small. At birth, the cranial region, which houses the brain, is disproportionally large relative to the bones of the face. This is evident by the fact that a newborn's head makes up about one-quarter of the body's total length, whereas in an adult, the head is only one-seventh of the total body length. The facial bones, including the maxilla and mandible, are underdeveloped and lack teeth at birth.
During early childhood, the facial structure undergoes substantial growth. Changes such as the enlargement of the mastoid process, the fusion of the mandible and frontal bone, the expansion of the paranasal sinuses, and the appearance of teeth contribute to the development and enlargement of the face. By the time a person reaches adulthood, the bones of the skull, which include the eight cranial bones, have fused together, providing a protective case for the brain and a structure for the face.