Viscerocranium

The term viscerocranium refers to the skull bones which contribute to the facial skeleton. Unlike the viscerocranium, those bones which surround the brain constitute the neurocranium (a.k.a. cranial cavity). Together, both viscerocranium and neurocranium, constitute the cranium.

The viscerocranium is formed of several bones, some are paired, while others are unpaired. Examples of paired bones include maxilla, zygomatic, nasal, lacrimal, palatine and inferior nasal concha bones. Unpaired ones include the vomer. Mandible, strictly speaking, is part of the skull, but not considered part of the cranium (cranium + mandible = skull).

Several bony cavities in the head can be seen opening into the facial skeleton. For instance, two cone-shaped bony chambers–called orbital cavities–can be seen with their bases face forwards onto the face, while the apices are directed posteromedially. They are situated immediately below the frontal aspect of the floor of the cranial cavity. The orbits contain the eyeballs and surrounding structures, including the extra-ocular muscles.

In addition, we can see the nasal cavities, which are sandwiched between the two orbital cavities and rest immediately above the oral cavity. Their walls are bony and cartilaginous and open anteriorly onto the face via the anterior nasal apertures (or nostrils), while communicate posteriorly with the nasopharynx via the posterior nasal apertures (or choanae). The nasal cavities extend laterally as four pairs of paranasal sinuses, into the bones of the cranial cavity and the facial skeleton.

Lastly, the oral cavity can be found immediately underneath the nasal cavities, from which it is separated via the hard and soft palate. Anteriorly, the oral cavity opens to the exterior as the mouth, while posteriorly it communicates with the oropharynx via the oropharyngeal isthmus.