occiput

The occiput, or occipital bone, is the posterior and inferior part of the skull. It forms the posterior cranial fossa and protects the lower brainstem and upper spinal cord. The bone has three main parts: a squamous (posterior) part, a basilar part at the skull base, and paired occipital condyles that project laterally near the foramen magnum. The foramen magnum, a large opening at the skull base, is a key feature that marks the transition between brain and spinal cord.

Prominent anatomical features include the foramen magnum, the external occipital protuberance with the superior and inferior nuchal lines for neck muscle attachments, and the hypoglossal canals that transmit CN XII. The occipital condyles rest on the Atlas (C1) to form the atlanto-occipital joints, which permit nodding movements. The occipital bone articulates with the parietal, temporal, and sphenoid bones at various sutures and contributes to the posterior cranial fossa. Inside the bone, grooves and canals accommodate vessels and nerves; the vertebral arteries enter the skull through the foramen magnum to join the basilar artery.

Developmentally, the occipital bone arises from occipital somites and part of the cartilaginous skull base. Clinically, injuries to the occipital bone or basilar skull fractures can affect the brainstem or cranial nerves. Occipital neuralgia involves pain in the occipital region due to irritation of the greater occipital nerve, and trauma to the occipital region can disrupt the atlanto-occipital joint or nearby vascular structures.