The occipital bone is the curved plate of bone that forms the back and base of your skull. It’s the bone you’d feel if you placed your hand on the lower back of your head, and it plays a critical structural role: it houses the opening where your brain connects to your spinal cord, supports the weight of your head on your spine, and anchors several major neck and scalp muscles.
Location and Basic Shape
The occipital bone sits at the very back and bottom of the skull. It curves from behind your ears, across the lower back of your head, and tucks underneath to form part of the skull’s floor. If you imagine the skull as a bowl, the occipital bone is the back wall and part of the base of that bowl. It connects to the two parietal bones above it, the temporal bones on either side, and a bone called the sphenoid at the skull’s base.
The Four Parts of the Bone
In adults, the occipital bone looks like a single piece, but it actually develops from separate sections that fuse together during childhood. These parts are arranged around the foramen magnum, the large hole at the bone’s center.
- Squamous part: The broad, curved plate behind the foramen magnum. This is the section you can feel at the back of your head. It forms the overhang at the rear of the skull.
- Basilar part: The thick section in front of the foramen magnum, sometimes called the base of the occiput. It sits deep inside the skull and connects to the sphenoid bone.
- Two lateral parts: These flank the foramen magnum on each side. They contain the occipital condyles, two smooth, rounded bumps that sit on top of the first vertebra in your neck and allow your head to nod up and down.
The Foramen Magnum
The foramen magnum is the most important feature of the occipital bone. It’s a large oval opening, roughly 3 centimeters wide, and it serves as the gateway between the brain and the spinal cord. The lowest part of the brainstem, called the medulla oblongata, passes through this hole and transitions into the spinal cord below.
It’s not just the spinal cord that uses this passageway. The vertebral arteries, which supply blood to the back of the brain, travel up through the foramen magnum. The anterior and posterior spinal arteries, which feed the spinal cord, also pass through. So does the spinal root of a nerve that controls muscles in the neck and shoulders, along with protective membranes (meninges) and several ligaments that stabilize the connection between skull and spine. Any condition that narrows or crowds this opening can compress these vital structures.
Ridges and Muscle Attachments
The back surface of the occipital bone isn’t smooth. It has two prominent horizontal ridges called the superior and inferior nuchal lines, and these serve as anchor points for muscles that move your head and scalp.
The superior nuchal line, the higher ridge, is where the trapezius muscle attaches (the large muscle running down the back of your neck and across your shoulders). The sternocleidomastoid, the thick muscle on each side of your neck that lets you turn your head, also attaches here, along with the occipital belly of the muscle that moves your scalp. The inferior nuchal line, closer to the foramen magnum, anchors a group of small, deep muscles that fine-tune head position and allow precise tilting and rotation. Between these ridges sits a small bump called the external occipital protuberance, the bony knob you can often feel at the center back of your skull.
These attachment sites matter practically because tension or strain in the muscles anchored here is a common source of headaches at the back of the head.
How the Bone Develops
At birth, the occipital bone isn’t a single fused structure. It exists as four independent pieces separated by cartilage, which gives the skull flexibility during delivery through the birth canal. The bone starts forming from five separate ossification centers during fetal development: the basilar part in front, two lateral parts on the sides, and two portions (upper and lower) that together make up the squamous part in back.
Fusion happens in stages. The two sections of the squamous part join with the lateral parts between ages 1 and 4. The basilar part fuses with the lateral parts later, between ages 3 and 6. By around age 6, the occipital bone has become one continuous piece. This fusion timeline can occasionally be relevant in pediatric imaging, where the cartilage gaps between unfused sections can be mistaken for fractures.
Chiari Malformation and the Posterior Fossa
The inner surface of the occipital bone forms a bowl-shaped space called the posterior fossa, which cradles the cerebellum (the brain region responsible for coordination and balance). When the occipital bone is smaller than expected, or the posterior fossa is too shallow, there isn’t enough room for the cerebellum. Under pressure, the lowest part of the cerebellum gets pushed downward through the foramen magnum into the spinal canal. This is called a Chiari malformation.
Symptoms can include headaches that worsen with coughing or straining, neck pain, balance problems, and numbness in the hands. The most common surgical treatment involves removing a small section of the occipital bone at the back of the skull to relieve pressure and give the cerebellum more room. This procedure, called posterior fossa decompression, essentially enlarges the bony space that was too small to begin with.
Fractures of the Occipital Bone
Because of its position, the occipital bone can fracture from direct blows to the back of the head or from high-energy trauma like car accidents and falls. Fractures at the base of the skull, called basilar skull fractures, are particularly serious because of the critical structures nearby.
Signs of a basilar fracture involving the occipital bone include bruising behind the ears (sometimes called Battle’s sign), cerebrospinal fluid leaking from the ears or nose, blood visible behind the eardrum, and nerve damage that can cause facial weakness or loss of hearing. These fractures don’t always show up on standard X-rays and often require a CT scan for diagnosis. Most heal without surgery, but those involving the foramen magnum or causing fluid leaks need close monitoring.