Final answer:
Fontanelles are absent in the adult skull. Sutures, zygomatic arch, and maxillary bone are present.
Step-by-step explanation:
Among the given options, fontanelles are absent in the adult skull. Fontanelles are soft spots on an infant's head, which are filled with fibrous connective tissue. They allow for the growth and expansion of the skull after birth. As an individual matures, the fontanelles gradually close and are replaced by solid bones.
On the other hand, sutures, zygomatic arch, and maxillary bone are present in the adult skull. Sutures are dense fibrous connective tissues that unite the adjacent skull bones, providing flexibility and allowing for growth. The zygomatic arch is a bony arch that spans from the cheek area to just above the ear canal. The maxillary bone is one of the bones forming the upper jaw.
In the newborn skull, fontanelles are large areas filled with fibrous connective tissue that have not yet ossified, allowing for growth of the skull and the underlying brain. As a person matures, these areas ossify, and by around the age of 2 years, the fontanelles are typically completely closed, leaving no fontanelles in the adult skull. The other options provided, including b) Sutures, c) Zygomatic arch, and d) Maxillary bone, are all present in the adult skull. Sutures are fibrous joints connecting the cranial bones, the zygomatic arch is a bony structure on the side of the skull, and the maxillary bone is one of the facial bones that form the upper jaw.