The human skull is composed of several bones that come together to protect the brain and support the structures of the face. The junctions where these bones meet are called sutures.

Sutures are immobile joints between adjacent bones of the skull. The narrow gap between the bones is filled with dense, fibrous connective tissue that unites the bones. The long sutures located between the skull bones are not straight but instead follow irregular, tightly twisting paths. These twisting lines tightly interlock the adjacent bones, strengthening the skull for brain protection.

There are four main sutures in the skull:

Coronal Suture: This suture runs horizontally across the skull, separating the frontal bone (at the front) from the parietal bones (on the sides). It extends from one side of the skull to the other, forming a continuous line.

Sagittal Suture: The sagittal suture is a vertical suture that runs along the midline of the skull. It separates the two parietal bones, which meet at the top of the skull. The sagittal suture extends from the anterior (front) fontanelle, also known as the bregma, to the posterior (back) fontanelle, known as the lambda.

Lambdoid Suture: The lambdoid suture is located at the back of the skull. It separates the parietal bones from the occipital bone. The lambdoid suture is named because its shape resembles the Greek letter "lambda" (Λ).

Squamosal Suture: This suture is formed by the junction of the temporal and the parietal bone on each side of the skull. It is located above the ear and has a squamous or scale-like shape.

At the intersection of four bones is the pterion, a small, capital-H-shaped suture line region that unites the frontal bone, parietal bone, squamous portion of the temporal bone, and greater wing of the sphenoid bone. It is the weakest part of the skull. The pterion is located approximately two finger widths above the zygomatic arch and a thumb's width posterior to the upward portion of the zygomatic bone.

During infancy and early childhood, the sutures are not fully fused to allow for the growth and expansion of the skull as the brain develops. These sutures contain fibrous connective tissue called cranial sutural or cranial vault sutural. This tissue allows for some flexibility and movement, facilitating brain growth and accommodating the rapid development of the skull.

As an individual matures, the sutures gradually close and fuse together in a process known as cranial ossification. By adulthood, the sutures have mostly fused, creating a rigid and stable structure. However, some small areas of the sutures may remain unfused throughout life; they are known as sutural bones or Wormian bones.

The study of sutures is important in various fields, such as anthropology, forensic science, and neurosurgery. By examining the patterns and morphology of sutures, scientists can gain insights into skull development, evolution, and potential abnormalities or pathologies associated with cranial sutures.

This text is adapted from https://openstax.org/books/anatomy-and-physiology-2e/pages/9-2-fibrous-joints