The viscerocranium (or splanchnocranium) is one of the two areas that make up the skull. It is situated anteriorly to the neurocranium which partly encapsulates it posteriorly, both from above and below.
The viscerocranium comprises several bones that form the skeleton of the face as well as parts of the jaw (facial skeleton).
Introduction to the Viscerocranium
The Nasal Bones
The nasal bones are a pair of bones that sit at the roof of the face and create the initial contour of the nose known as the bridge of the nose. They meet in the midline with one another and additionally articulate with the frontal bone superiorly via the frontonasal suture and the maxilla laterally via the nasomaxillary sutures.
The maxilla makes up the largest portion of the face and has the most muscle tissue attached to it, which is responsible for facial expressions. As with the nasal bones, it also connects to all the bones within the bony orbit (except the frontal bone).
The Zygomatic Bones
The zygomatic bone is the bridge between the neurocranium and the viscerocranium. It forms the lateral prominences of the face (“cheekbones”) where the zygomatic and temporal portions of the zygomatic arch meet each other. It also articulates with the maxilla via the zygomaticomaxillary suture and the frontal bone via the frontozygomatic suture. Inside the bony orbit it contacts the frontal bone, the sphenoid bone and the maxilla.
The Lacrimal Bones
The lacrimal bone can be found on the medial wall of the bony orbit. It houses the lacrimal sac and supports the contents of the eye socket. Anteriorly it is surround by the maxilla, superiorly by the frontal bone and posteriorly by the ethmoid bone.
The Ethmoid Bone
The ethmoid bone consists of a horizontal and a vertical plate. From the bony orbit only the vertical plate can be seen on the medial wall. It cascades down from the roof of the nasal cavity and separates it into two nasal passages. Its appendages include the superior and middle nasal conchae. Within the bony orbit it is surrounded anteriorly by the lacrimal bone, superiorly by the frontal bone, inferiorly by the maxilla and the orbital process of the palatine bone and posteriorly by the sphenoid bone.
The vomer is part of the nasal septum which follows the midline of the viscerocranium and creates the division between the two symmetrical sides of the nasal cavity. To be exact, the vomer forms the posterior inferior aspect of the septum in between the perpendicular plate of the ethmoid bone anterosuperiorly and the palatine bone posteroinferiorly.
The Sphenoid Bone
The greater and lesser wings of the sphenoid bone make up the posterior wall of the bony orbit. They contain all three orifices including the optic canal and the superior and inferior orbital fissures. The sphenoid bone is surrounded by and in contact with all of the bones that make up the bony orbit.
The Palatine Bones
The palatine bone is a paired, L-shaped bone that is found interposed between the maxilla and sphenoid bones. It is primarily defined by its horizontal and perpendicular plates. The horizontal plate forms the posterior portion of the hard palate of the oral cavity and is directly inferior to the nasal cavity. The perpendicular plate contributes to the lateral wall of the nasal cavity where it borders the pterygoid process of sphenoid bone.
The palatine bone also contributes to a small portion of the orbital floor, via the orbital process found at the superior end of the perpendicular plate.
The mandible forms the chin and the jaw line contours of the face and allows a person to speak, chew and open their mouth. To be precise, the mandible is not part of the skull but a separate bone that articulates with it through the temporomandibular joint (TMJ). Nevertheless it should be mentioned when discussing facial bones.
In this article, we explored the bones of the viscerocranium which included:
- the nasal bones, which form the bridge of the nose.
- the maxillae - the large anterior bilateral bones of the viscerocranium, which provide attachment for several muscles of facial expression
- the zygomatic bones - more commonly known as the 'cheek bones'
- the lacrimal bones - small paired bones posterior to the maxillae which form the nasolacrimal ducts.
- the ethmoid bone - the irregular shaped bone, which contributes to several bony structures of the nasal cavity.
- the vomer- a flat, vertical bone which forms a portion of the nasal septum, posterior to the perpendicular plate of the ethmoid bone.
- the sphenoid bone - the 'keystone' to the cranium as a whole. It contributes to several bony landmarks and surfaces of the cranium e.g. posterior wall of the orbit
- the palatine bones, which form the the posterior portion of the hard palate.
- the mandible - the 'jaw' bone, which houses the teeth of the mandibular dental arch.