A cranial suture is a fibrous joint that connects the bones of the skull. These joints are flexible in early life, allowing for the growth of the brain and flexibility during birth. The squamous suture is located on the lateral (side) aspect of the human cranium. It runs along the side of the head, dividing the upper and lower portions of the skull’s sidewall, and provides protection to underlying neurovascular structures.
Precise Anatomical Location
The squamous suture is situated bilaterally on both sides of the skull. It follows a distinct, semi-circular path, beginning near the front of the head and arcing upward and backward. The suture starts at the Pterion, a junction point where four skull bones meet, and extends posteriorly.
It curves superiorly (upward) and then sweeps posteriorly and inferiorly (backward and downward) across the side of the head. This path defines the superior boundary of the temporal fossa, which is the shallow depression on the side of the skull above the cheekbone. Its trajectory places it directly above the external acoustic meatus (the opening to the ear canal). The suture continues toward the back of the skull, meeting the parietomastoid suture near the mastoid angle of the parietal bone. This placement makes the squamous suture a consistent surface bony landmark.
Articulating Skeletal Components
The squamous suture is the site where the parietal bone and the temporal bone join together. This junction occurs between the inferior border of the parietal bone and the superior edge of the temporal bone. The temporal bone component involved is its thin, fan-shaped upper portion, known as the squamous part of the temporal bone.
The Pterion Junction
The suture line extends anteriorly to the Pterion, a complex junction point. At the Pterion, the squamous suture contributes to the articulation of four different bones:
- The parietal bone
- The frontal bone
- The greater wing of the sphenoid bone
- The squamous part of the temporal bone
Posteriorly, the squamous suture transitions into the parietomastoid suture, where the parietal bone meets the mastoid process of the temporal bone.
Unique Beveled Structure
The defining characteristic of the squamous suture is its unique morphology, which is unlike the interlocking, jagged edges found in most other cranial sutures. This joint is classified as a squamous type of suture, derived from the Latin word meaning “scale.” The bones forming this boundary overlap significantly, similar to roof shingles.
This structure is a beveled articulation where the inferior edge of the parietal bone overlaps the superior edge of the temporal bone. This overlapping design results in a greater surface area of contact between the two bones compared to a simple butt joint. The enhanced contact allows for a degree of movement and flexibility. This flexibility helps to absorb and dissipate mechanical forces, such as those caused by impacts or mastication. The suture may not fully fuse until around 60 years of age, indicating its long-term functional role in cranial dynamics.