The parietal bones (Latin : ossa parietalia, verticis, bregmatis ; french : os pariétal) form a principal part of the roof of the skull; they are of a square form, convex externally, concave internally, and present each two surfaces and four borders. The external surface, rises towards its middle, where it presents a slight elevation, called the parietal eminence, 5 below which is a curved line, forming part of the temporal ridge, and bounding a flat surface (planum semicirculare), which forms a part of the temporal fossa. At the upper and back part of the bone, usually about two lines from the sagittal suture, is a small hole, 6 (foramen parietale) which transmits a communicating vein; its position is exceedingly variable; even its existence is not constant.
The internal surface of the bone, is marked by branching lines (sulci meningei), corresponding with the course of the middle meningeal artery, and by depressions (impressiones digitatal) for the convolutions of the brain. Towards its middle is a depression, "parietal fossa," corresponding with the eminence (parietal) on the outside.
Along the superior border is a slight depression, 5 which with a similar one in the corresponding bone forms a groove adapted to the course of the longitudinal sinus; and in the same situation (in most skulls, particularly those of old persons) are some small pits (foveas glandulares), corresponding with the so-named glandulas Pacchioni.
The superior border is straight, and articulated with its fellow by a series of dentations ; the inferior border, concave and bevelled off at its outer margin, is overlapped by the squamous portion of the temporal bone ; the anterior unites with the frontal bone, and the posterior with the occipital.
The anterior inferior angle, 7 dips down to the great wing of the sphenoid bone, and presents a groove, 7 internally for the middle meningeal artery: the posterior inferior angle, 8 articulates with the mastoid part of the temporal bone, and presents internally a small part of the groove which lodges the lateral sinus.
Each parietal bone gives attachment to the temporal muscle by that part of its surface which lies beneath the temporal ridge (planum semicirculare): the remainder of its outer surface is covered by the aponeurosis of the occipito-frontalis.
It articulates with its fellow of the opposite side, and with the frontal, the sphenoid, the temporal, and the occipital bones.
Its growth proceeds from one ossific centre, which cor- responds with the parietal eminence, and is first perceptible about the same time that ossification begins in the spinal column. At birth the antero-superior angles of these bones are not developed ; hence there exists an interval between them and the still divided os frontis, which is called the " fontanelle" (fons, bregma).
View of the internal Internal surface of the parietal bone