Give an account on the structures of skull.

Explanation

The skull is composed of two sets of bones, cranial and facial bones . It consists of 22 bones of which 8 are cranial bones and 14 are facial bones . The cranial bones form the hard protective outer covering of the brain and called the brain box. The capacity of the cranium is `"1500 cm"^(3)`. These bones are joined by sutures which are immovable. They are a paired parietal, paired temporal and individual bones such as the frontal, sphenoid, occipital and ethmoid.

The large hole in the temporal bone is the external auditory meatus. In the facial bones maxilla, zygomatic, palatine, lacrimal, nasal are paired bones whereas mandible or lower jaw and vomer are unpaired bones. They form the front part of the skull. A single U-shaped hyoid bone is present at the base of the buccal cavity. It is the only one bone without any joint. Each middle ear contains three tiny bones-malleus, incus and stapes collectively are called ear ossicles. The upper jaw is formed of the maxilla and the lower jaw is formed of the mandible. The upper jaw is fused with the cranium and is immovable. The lower jaw is connected to the cranium by muscles and is movable. The most prominent openings in the skull are the orbits and the nasal cavity . Foramen magnum is a large opening found at the posterior base of the skull. Through this opening the medulla oblongata of the brain descends down as the spinal cord.