What Is an Occipital Bun?

The skull, also referred to as the cranium, is part of the skeletal system and consists of a collection of twenty-two different bones designed to protect the brain. It also gives shape and support to the face. Broken into two sections, the skull bones are divided into facial bones and cranial bones. The occipital bun, also known as the occiput or occipital bone, is an important cranial bone.

Located in the back of the head, the occipital bun is a curved trapezoid with two parallel sides. This unique shape gives the back of the head its rounded contour. Like the skull bones, the occiput is divided into different regions or sections: the basilar segments, the lateral segments, and the squama occipitalis.

The basilar region of the occipital bun spreads forward and upward. On the lower portion there is a nodule called the pharyngeal tubercle, a fibrous ridged union where the superior pharyngeal constrictor muscle attaches. This muscle aids in the movement of food down into the esophagus.

The lateral sections are located on either side of the occipital bun. Condyles — or kidney-shaped projections — positioned on this part of the occiput allow for the skull to attach to the atlas, the first cervical or neck spinal bone. At the base of each condyle there is short canal or tunnel called the hypoglossal canal. The hypoglossal canal houses the hypoglossal nerve which supplies sensations and motor signals to the tongue.

In the occipital bun there is a gap or opening. This oval break in the bone, called the foramen magnum, is an important structure for opening and maintaining the communication system between the brain and spinal cord. Housing the medulla oblongata — the lower portion of the brainstem — along with several essential arteries, nerves and ligaments, this hole allows the brain to send and receive messages transmitted to and from the body through the spinal cord. The squama occipitalis, or squama of the occipital bun is located above and behind the foramen magnum.

The squama occipitalis of the occipital bun is an important structure for the attachment of muscles. These muscles, such as the sternocleidomastoid, occipitalis and trapezius, link the head to the neck. Attachments are made by the presence of key features of this section of the bone, such as the external occipital protuberance, a nodule in the middle of the squama, and the presence of nuchal lines, four curved lines located on its surface.