The structure indicated is the squamous suture of the skull.
Sutures are junctions between the bones of the skull – they are a type of fibrous joint, bound together by Sharpey’s fibres.
The squamous suture forms the joint of the skull between the squamous part of the temporal bone and the inferior aspect of the parietal bone. Posteriorly, the squamous suture becomes the parietomastoid suture where the mastoid process articulates with the parietal bone. Anteriorly, the squamous suture extends towards pterion.
Learn more about the sutures of the skull in this tutorial.