Norma Occipitalis- Skull Exterior

Norma occipitalis is convex upwards and on each side and is flattened below.

Bone Seen in norma occipitalis

1. Posterior part of the parietal bones, above.

2. The upper part of the squamous part of the occipital bone below.

3. Mastoid part of the temporal bone, on each side.

Sutures

An immovable junction between two bones, such as those of the skull.

1. The lambdoid suture lies between the occipital bone and the two parietal bones. Sutures or wormain bones are common along this suture.

2. The ocipitomastoid suture lies between the occipital bone and mastoid part of the temporal bone.

3. The parietomastoid suture lies between the parietal bone and mastoid part of the temporal bone.

4. The posterior part of the sagittal suture is also seen.

Other features of norma occipitalis

1. Lambda, parietal foramina, and obelion have been examined in the norma verticalis.

2. The external occipital protuberance is a median prominence in the lower part of this norma. It marks the junction of the head and the neck. The most prominent point on this protuberance is called the inion.

3. The superior nuchal lines are curved bony ridges passing laterally from the protuberance. These also mark the junction of the head and the neck. The area below the superior nuchal lines will be studied with the norma basalis.

4. The highest nuchal lines are not always present. They are curved bony ridges situated about 1 cm above the superior nuchal lines. They begin from the upper part of the external occipital protuberance and are more arched than the superior nuchal lines.

5. The occipital point is a median point a little above the inion. It is the point farthest from the glabella.

6. The mastoid (Greek breast) foramen is located on the mastoid part of the temporal bone at or near the occipitomastoid suture. Internally, it opens at the sigmoid sulcus. The mastoid foramen transmits an emissary vein and the meningeal branch of the occipital artery.

7. The interparietal bone (inca bone) is occasionally present. It is a large triangular bone located at the apex of the squamous occipital. This is not a sutural or accessory bone but represents the membranous part of the occipital bone which has failed to fuse with the rest of the bone.