Os occipitale

The occipital bone is a cranial bone and part of the neurocranium.

Anatomy

The occipital bone is bordered superiorly by the Sutura lambdoidea, which separates it from the two Ossa parietalia; laterally by the Os temporale; and inferiorly by the Os sphenoidale.

The occipital bone consists of several anatomical sections that together form a complex structure[^1]:

Basilar part

The basilar part is located ventral to the Foramen magnum and adjacent to the petrous part of the temporal bone. Ventrally, the basilar part fuses with the sphenoid bone during puberty (os tribasilare), thereby forming the Clivus. The superior pharyngeal constrictor muscle and the pharyngeal raphe attach to the pharyngeal tubercle, which is located on the inferior surface of the basilar part. The surface of the basilar part is smooth and, on its inner aspect, presents the clival region, which plays a central role in skull base surgery.

Lateral part

The bilateral lateral parts, also called the condylar parts, are located lateral to the foramen magnum. Both sides have a kidney-shaped process, the Condylus occipitalis, which articulates with the first cervical vertebra via the atlanto-occipital joint. Dorsally lies the Canalis condylaris, through which the condylar emissary vein passes, connecting the external vertebral venous plexus with the Sinus sigmoideus. The Nervus hypoglossus passes through the Canalis nervi hypoglossi, which runs through the lateral part of the occipital bone.

Squamous part

The squamous part is the largest portion of the occipital bone. A palpable bony prominence at the midline of the external surface of the bone, the Protuberantia occipitalis externa, serves as the origin of the trapezius muscle. In addition, the external surface has three arched bony ridges, known as the nuchal lines:

• The Linea nuchae suprema runs above the external occipital protuberance and serves as the attachment site for the epicranius muscle and the Galea aponeurotica.

• The Linea nuchae superior runs slightly inferior to it. It provides attachment for the trapezius, Musculus sternocleidomastoideus, and splenius capitis muscles.

• The Linea nuchae inferior runs slightly lower, and the semispinalis capitis muscle attaches superior to it.

On its inner aspect, the squamous part of the occipital bone has depressions formed by intradural venous channels: the Sinus sagittalis superior, the Sinus transversi, and the Sinus sigmoideus. Superior to the Sulcus sinus transversus is a depression for the cerebral Lobus occipitalis, and the Cerebellum lies in the depression below it.

Figure