The following diagrams (RF Hoyt) represent the appearance of the skull in various planes of section (e.g. coronal) to reinforce the concept of cranial spaces and the borders they share.
Whereas the cranial portion of the skull (neurocranium) lodges the brain, the facial skeleton has evolved to house the visual, olfactory, and gustatory organs and to frame the entrance to both respiratory and digestive systems (tracts).
The physical arrangement of spaces within the facial skeleton – with one another, with the paranasal air sinuses, and with the anterior and middle cranial fossae – is of great clinical importance. It also makes study of the skull much easier.
Many basic spatial relationships in a coronal plane through the anterior region of the face are obvious if one looks thoughtfully into a mirror and applies a little self-knowledge. Begin by realizing that the frontal bone forms not only the floor of the anterior cranial fossa, but also the roof of the orbit. It should be apparent that there are two nasal cavities, separated by the nasal septum along or close to the midline. Each cavity is tall and narrow, its roof the floor of the anterior cranial fossa along side the crista galli, its floor the hard palate, which separates it from the oral cavity. The paired nasal cavities stretch from the nostrils (nares, anterior nasal apertures) back above the hard palate to the posterior nasal apertures, the choanae.
Each nasal cavity is flanked laterally by the orbit, which lies immediately below the anterior cranial fossa and thus immediately in front of the middle cranial fossa. The maxillary air sinus also flanks the nasal cavity. It lies below the floor of the orbit and immediately above the roots of the upper teeth.
Spatial relationships deeper in the face are not easily appreciated on superficial inspection. They can, however, be understood from a coronal section taken just behind the maxillae.
The zygomatic arch is level with the infratemporal crest of the sphenoid. A plane passed through these two landmarks separates the temporal fossa (above, TF) from the infratemporal fossa (below, ITF).
The small pterygopalatine fossa lies in front of the pterygoid process of the sphenoid, medial to the infratemporal fossa. It can be reached through the pterygomaxillary fissure, between the maxilla and the pterygoid process. It is lateral to the nasal cavity.
The anterior cranial fossa lies above the orbit, and both are medial to the temporal fossa.
The body of the sphenoid bone, occupied by the sphenoid air sinus, lies behind the upper part of the nasal cavities.
Additional relationships can be seen in a parasagittal section passing through the superior orbital fissure and the base of the greater wing of the sphenoid.
Anteriorly, the orbit lies below the anterior cranial fossa, the maxillary sinus lies below the orbit, and the oral cavity lies below the maxillary sinus.
Posteriorly, the middle cranial fossa lies behind the orbit and above the infratemporal fossa.
The pterygopalatine fossa lies between the maxillary sinus and the pterygoid process of the sphenoid. It is below the floor of the middle cranial fossa and below and behind the apex of the orbit.