Facial skeleton

The facial skeleton is a specialized group of bones. These bones connect to build a specific portion of the skull. The rest of the skull is known as the neurocranium. While the neurocranium protects the brain, the facial skeleton forms the structure of the face. In human anatomy, scientists sometimes call this group the membranous viscerocranium. This term includes the mandible and other dermatocranial elements. These elements are distinct because they are not part of the braincase.

There are fourteen individual bones that comprise the human facial skeleton. Two lacrimal bones are located near the eyes. Two nasal bones form the bridge of the nose. The maxilla consists of two bones that form the upper jaw. Because these maxillary bones are fused, they are often listed as one bone. Two zygomatic bones create the cheekbones. Two palatine bones are located within the mouth. Two inferior turbinal bones sit inside the nasal cavity. Finally, there is the mandible, which is the lower jaw. The vomer is a single bone found in the face.

Anatomists sometimes debate which bones belong to the facial skeleton. Some researchers include elements of the cartilaginous viscerocranium. The hyoid bone is a common example of such an element. Others may include the ethmoid bone or the sphenoid bone. However, these two bones are also frequently classified as part of the neurocranium. The mandible is another unique case in classification. It is generally considered separately from the cranium itself.

The development of these bones is a complex biological process. The facial skeleton is composed of dermal bone. These bones derive from neural crest cells during development. These same neural crest cells are responsible for making teeth. They also contribute to the development of the adrenal medulla. Some facial bones also come from the sclerotome. The sclerotome is derived from the somite block of the mesoderm.

Bone formation processes can vary between different types of animals. In Chondricthyes, which are cartilaginous vertebrates, bone development follows different rules. In these animals, the bones are not replaced via endochondral ossification. This is a different method of bone growth than what occurs in many other vertebrates. Understanding these developmental pathways helps scientists see how different species evolved.

Every human has a unique craniofacial form. These variations in shape are largely due to patterns of biological inheritance. Scientists use cross-analysis to study these differences. They look at osteological variables and genome-wide SNPs. This research has identified specific genes that control how the face develops. These genes act as instructions for the growing skeleton.

Specific genes are responsible for different facial features. The genes DCHS2, RUNX2, GLI3, PAX1, and PAX3 are very important. These five genes determine the morphology, or shape, of the nose. Another gene called EDAR plays a different role. The EDAR gene impacts how much the chin protrudes. By studying these genes, we learn how tiny biological instructions create the diverse faces we see in the world.