|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
|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 lambdoidal, while the sagittal lies in the medial plane between the parietal bones.|
Upper Surface of the Base of the Skull (Fig. 193).
| The upper surface of the base of the skull or floor of the cranial cavity presents three fossæ, called the anterior, middle, and posterior cranial fossæ.|
Anterior Fossa (fossa cranii anterior).The floor of the anterior fossa is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the small wings and front part of the body of the sphenoid; it is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. It is traversed by the frontoethmoidal, sphenoethmoidal, and sphenofrontal sutures. Its lateral portions roof in the orbital cavities and support the frontal lobes of the cerebrum; they are convex and marked by depressions for the brain convolutions, and grooves for branches of the meningeal vessels. The central portion corresponds with the roof of the nasal cavity, and is markedly depressed on either side of the crista galli. It presents, in and near the median line, from before backward, the commencement of the frontal crest for the attachment of the falx cerebri; the foramen cecum, between the frontal bone and the crista galli of the ethmoid, which usually transmits a small vein from the nasal cavity to the superior sagittal sinus; behind the foramen cecum, the crista galli, the free margin of which affords attachment to the falx cerebri; on either side of the crista galli, the olfactory groove formed by the cribriform plate, which supports the olfactory bulb and presents foramina for the transmission of the olfactory nerves, and in front a slit-like opening for the nasociliary nerve. Lateral to either olfactory groove are the internal openings of the anterior and posterior ethmoidal foramina; the anterior, situated about the middle of the lateral margin of the olfactory groove, transmits the anterior ethmoidal vessels and the nasociliary nerve; the nerve runs in a groove along the lateral edge of the cribriform plate to the slit-like opening above mentioned; the posterior ethmoidal foramen opens at the back part of this margin under cover of the projecting lamina of the sphenoid, and transmits the posterior ethmoidal vessels and nerve. Farther back in the middle line is the ethmoidal spine, bounded behind by a slight elevation separating two shallow longitudinal grooves which support the olfactory lobes. Behind this is the anterior margin of the chiasmatic groove, running lateralward on either side to the upper margin of the optic foramen.
The Middle Fossa (fossa cranii media).The middle fossa, deeper than the preceding, is narrow in the middle, and wide at the sides of the skull. It is bounded in front by the posterior margins of the small wings of the sphenoid, the anterior clinoid processes, and the ridge forming the anterior margin of the chiasmatic groove; behind, by the superior angles of the petrous portions of the temporals and the dorsum sellæ; laterally by the temporal squamæ, sphenoidal angles of the parietals, and great wings of the sphenoid. It is traversed by the squamosal, sphenoparietal, sphenosquamosal, and sphenopetrosal sutures.
| The middle part of the fossa presents, in front, the chiasmatic groove and tuberculum sellæ; the chiasmatic groove ends on either side at the optic foramen, which transmits the optic nerve and ophthalmic artery to the orbital cavity. Behind the optic foramen the anterior clinoid process is directed backward and medialward and gives attachment to the tentorium cerebelli. Behind the tuberculum sellæ is a deep depression, the sella turcica, containing the fossa hypophyseos, which lodges the hypophysis, and presents on its anterior wall the middle clinoid processes. The sella turcica is bounded posteriorly by a quadrilateral plate of bone, the dorsum sellæ, the upper angles of which are surmounted by the posterior clinoid processes: these afford attachment to the tentorium cerebelli, and below each is a notch for