The human skull is more than just one large bone. It is made up of several interconnected bones, some of which occur in right and left pairs. The parietal bone actually refers to either of the two flat bones on the right and left sides of the head. They are large bones that together form the top and sides of the skull. The parietal bones lie over the parietal lobe on either side of the brain.
These bones make up two of the eight cranial bones, which together enclose and protect the brain. Other cranial bones include the left and right temporal bones, the frontal bone, the occipital bone, the sphenoid and the ethmoid bone. Cranial bones are connected by fibrous joints called sutures. In newborns up until approximately age two, these joints are formed by soft membranes called fontanels; the flexibility of the fontanels allows for bone and brain growth. As we mature, the sutures become more rigid, greatly reducing the amount of movement that can occur between the cranial bones.
The parietal bone is shaped roughly like a curved rectangle. At the top, the left parietal bone connects with the right one to form the sagittal suture at the roof of the skull. Towards the front of the skull, both parietals connect to the frontal bone at the coronal suture. At the lower edge, the parietals meet the temporal bones, one near each ear, as well as the sphenoid bone which runs behind the eyes. The back portion of the parietal bone connects to the occipital bone, which forms the back of the skull.
Like many other bones, the primary function of this bone is to provide protection of vital tissues and organs, in this case, the brain. The interior surface also contains numerous grooves and channels that protect the major arteries that supply oxygen and nutrients to the brain. It also works with the other cranial bones and structures to protect the vital nerve functions that originate in the brain and cause nearly every function of the body, both voluntary movement and involuntary actions such as breathing.
These bones are commonly used as bone graft donor sites when a patient needs reconstructive surgery, particularly facial surgery. The surgeon removes a portion of the parietal bone and grafts it onto the area that needs to be reconstructed. Parietal bones are preferred because of their thickness, their proximity to the surface of the body, and because the harvest site tends to heal more quickly than other common donor sites, such as the ribs or hips. Additionally, harvesting the patient's own bone tissue greatly reduces the risk of rejection after surgery.