The outer surface of the skull possesses a number of landmarks. The point at which the frontal bone and the two parietal bones meet is known as the bregma. The point at which the two parietal bones and the occipital bone meet is known as the lambda. Not only do these landmarks indicate the
fontanelle in newborns, they also act as reference points in medicine and surgery. The inner surface of the skull-cap is concave and presents depressions for the convolutions of the
cerebrum, together with numerous furrows for the lodgement of branches of the meningeal vessels. Along the middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its margins afford attachment to the
falx cerebri. On either side of it are several depressions for the
arachnoid granulations, and at its back part, the openings of the
parietal foramina when these are present. It is crossed in front by the
coronal suture and behind by the
lambdoid suture, while the
sagittal suture lies in the medial plane between the parietal bones.
Layers and inner layer. Most bones of the calvaria consist of internal and external tables or layers of compact bone, separated by
diploë. The diploë is cancellous bone containing red
bone marrow during life, through which run canals formed by
diploic veins. The diploë in a dried calvaria is not red because the protein was removed during preparation of the cranium. The internal table of bone is thinner than the external table, and in some areas there is only a thin plate of compact bone with no diploë. Calvarial bones are supplied by endosteal and periosteal sheaths which are innervated by the nociceptors, sensory, sympathetic, and parasympathetic nerves. Horizontal section of the mouse pups showed that the density of nerve fibers was highest in the region of forehead, temples, and the back of head which crossing the frontal, parietal, and interparietal bones. In the calvarial innervation in the adult mouse, CGRP-labeled fibers and peripherin were seen in the sutures, emissary canals, and bone marrow but not in diploe. Nerve fibers passing through the emissary canals and cavity of bone marrow provided the branches of periosteal and dural nerves whereas fibers from the sutures gave out to the dural nerves. File:Gray769.png File:Gray1196.png ==Development==