Final answer:
Fontanelles are the unique structures in the fetal skull that provide additional space for molding the head shape as the baby passes through the birth canal.
Step-by-step explanation:
The unique structures in the fetal skull that provide additional space for molding the head shape as the baby passes through the birth canal are called fontanelles. Fontanelles are large areas of fibrous connective tissue that separate the bones of the skull and allow for continued growth and expansion of the skull after birth.