Occipital aspect of cranium

The back part of the skull, known as the occipital aspect of cranium or norma occipitalis, refers to how the skull appears from behind. The bones involved in this view include the upper parts of the parietal bones above, the upper portion of the squamous part of the occipital bone below, and the mastoid portion of the temporal bone on each side.

These bones are connected to each other through joints known as sutures. For instance, the occipital bone at the back connects with the two parietal bones through a suture called the lambdoid suture, which runs from side to side. On the sides, the lambdoid suture appears to divide into two sutures: the occipitomastoid suture between the occipital and mastoid bones, and the parietomastoid suture between the parietal and mastoid bones. Additionally, the posterior portion of the midline sagittal suture can also be observed on the occipital aspect of cranium.

Some notable features on the posterior view of the skull include two parietal foramina located on each side of the sagittal suture, which are visible when viewing the skull from behind. These foramina allow emissary veins from the scalp to drain into the superior sagittal sinus. The point on the sagittal suture between the two parietal foramina is called obelion. Moving further back and down, we can see a point called lambda, which marks the meeting point of the sagittal and lambdoid sutures.

Continuing downward, we notice a central bony prominence known as the external occipital protuberance. The most prominent part of this protuberance is called inion. On either side, there are bony ridges extending sideways from the external occipital protuberance called the superior nuchal lines. Together, the external occipital protuberance and the superior nuchal lines mark the junction between the head and neck regions.

There are several muscles attached in this area. The trapezius muscle originates from the external occipital protuberance and the inner part of the superior nuchal line. On the lateral side, we find the insertion of the sternocleidomastoid muscle of the neck, situated on the superior nuchal line. The occipital belly of the occipitofrontalis muscle, a scalp muscle, attaches to the skull just above the superior nuchal line. Lastly, a ligament called the ligamentum nuchae is connected to the lower end of the external occipital protuberance.

On each side, near the occipitomastoid suture, there is a small mastoid foramen that allows for the passage of an emissary vein and the meningeal branch of the occipital artery.