11.3:
Cranial Bones: Superior and Posterior View
The skull's superior view is dominated by the frontal and parietal bones.
The frontal bone forms the forehead with thick supraorbital margins and foramina lying under the eyebrows. In between the margins is the glabella, a smooth region.
The frontal bone meets the paired parietal bones at the coronal suture. These paired parietal bones, covering the skull's top and sides, are joined by the sagittal suture.
Forming the posterior part and most of the base of the skull is the occipital bone. It connects to the parietal bones via the lambdoid suture. A midline projection, the external occipital protuberance, secures a large elastic ligament — ligamentum nuchae, which helps support the head.
The superior and inferior nuchal lines are laterally extending ridges that allow muscle attachment.
At the base, through the opening called the foramen magnum, the brain connects with the spinal cord.
On each side of the foramen, the occipital condyles, curved projections, articulate with the first vertebra.
11.3:
Cranial Bones: Superior and Posterior View
The superior view of the cranium shows the frontal and paired parietal bones.
The frontal bone is the single bone that forms the forehead. At its anterior midline, between the eyebrows, there is a slight depression called the glabella. The frontal bone also forms the supraorbital margin of the orbit. Near the middle of this margin is the supraorbital foramen, the opening that provides passage for a sensory nerve to the forehead. The frontal bone is thickened just above each supraorbital margin, forming rounded brow ridges. These are located just behind the eyebrows and vary in size among individuals, although they are generally larger in males. Inside the cranial cavity, the frontal bone extends posteriorly. This flattened region forms both the roof of the orbit below and the floor of the anterior cranial cavity above.
The parietal bones form most of the upper lateral sides of the skull. These are paired bones, with the right and left parietal bones joining together at the top of the skull. Each parietal bone is also bounded anteriorly by the frontal bone, inferiorly by the temporal bone, and posteriorly by the occipital bone.
The posterior view of the skull is dominated by the occipital bone, which forms the posterior base of the cranial cavity. On its outside surface, at the posterior midline, is a small protrusion called the external occipital protuberance, which serves as an attachment site for a ligament of the posterior neck. Lateral to either side of this bump is a superior nuchal line (nuchal = "nape" or "posterior neck"). The nuchal lines represent the most superior point at which muscles of the neck attach to the skull, with only the scalp covering the skull above these lines. On the base of the skull, the occipital bone contains the large opening of the foramen magnum, which allows for the passage of the spinal cord as it exits the skull. On either side of the foramen magnum is an oval-shaped occipital condyle. These condyles form joints with the first cervical vertebra, and so support the skull on top of the vertebral column.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 7.2: The Skull