c. Inferior Aspect. The inferior, or basal, aspect of the skull (figure 2-30)
presents the following bony parts, passing from the anterior to the posterior aspects.
The palatine processes of the maxillae and the horizontal plates of the palatine bones
form the hard palate, or roof, of the mouth. The bones that compose the hard palate
fuse at the median palatine suture. The posterior portion of the vomer can be seen.
The occipital bone, situated at the back and base of the skull, presents the foramen
magnum, the squama, and the occipital condyles. Extending posteriorly and laterally
from the foramen magnum, is a flat, expanded part named the squama, on which is the
external occipital protuberance (EOP). The temporal bones are situated at the sides
and base of the skull. The following structures of the temporal bones are visible. The
apex of each mastoid tip is situated laterally. Anterior to the mastoid tip is the glenoid
(or mandibular) fossa. The styloid process is anterior and medial to the mastoid tip.
Extending anteromedially from the base of the styloid process to the basilar portion of
the occipital bone is the petrous portion of the temporal bone.
2-32. INTERIOR OF THE CRANIAL CAVITY
The floor of the cranial cavity (figure 2-31) presents three fossae: the anterior, the
middle, and the posterior cranial fossae.
a. Anterior Cranial Fossa. The floor of the anterior cranial fossa, which
supports the frontal lobes of the brain, is formed by the frontal, ethmoid, and sphenoid
bones. The lateral portions of the anterior fossa correspond to the roofs of the orbits.
The medial portion corresponds to the roof of the nasal cavity.
b. Middle Cranial Fossa. The middle cranial fossa, which is deeper than the
anterior fossa, consists of a central (or medial) portion and two lateral portions. Situated
centrally is the body of the sphenoid. The lateral parts of the middle cranial fossa are of
considerable depth and support the temporal lobes of the brain. They are bounded
anteriorly by the posterior margins of the lesser wings of the sphenoid, and the orbital
plates of the frontals. They are bounded posteriorly by the petrous portions of the
temporals, and laterally by the squama of the temporals, the parietals, and the greater
wings of the sphenoid.
c. Posterior Cranial Fossa. The dorsum sellae of the sphenoid bone and the
petrous portions of the temporal bones separate the posterior cranial fossa from the
middle cranial fossa. It is the largest and deepest of the three fossae and lodges the
cerebellum, pons, and medulla oblongata.