Cigomatic Bone: Function, Medical Considerations and Evolution of the Zygomatic Bow

Definition:

The zygomatic bones are located in the upper and lateral parts of the face. Each one forms the prominence of the cheek and contributes to the formation of the lateral wall and the floor of the orbit, and the temporal and infratemporal pits.

The zygomatic bone has a somewhat quadrangular shape, but it has a flange-shaped projection from the anterior part of its medial aspect. It has three surfaces, five edges, and two processes.

The lateral surface (malar), directed laterally and forward, is convex and is drilled near its orbital edge by the facial zygomatic foramen (which is often double) for the passage of the zygomatic nerve and facial vessels.

Below this foramen, a slight elevation gives rise to the minor zygomatic (zygomatic head of the Latin quadratus labii superiors), and later the zygomatic major takes its origin.

The medially and the backwardly directed temporal surface is concave, previously presenting a rough area for articulation with the maxilla.

Subsequently, a soft concave area extends upwards on the posterior face of the frontal process to form the anterior limit of the temporal fossa and backward on the medial aspect of the material process to create an incomplete lateral wall for the infra-temporal fossa.

 

The temporal, zygomatic foramen, for the transmission of the nerve of the same name, perforates this surface near the base of the frontal process.

The smooth and concave orbital surface forms the anterolateral part of the floor and the contiguous part of the lateral wall of the orbit, extending upwards on the medial aspect of the frontal process.

Usually, it presents the orifices of two conduits, called zygomatic-orbital, leading to the facial zygomatic and the other to the temporal zygomatic foramen.

The anterosuperior orbital border is smooth and concave and forms a considerable part of the circumference of the orbital opening, below and on the lateral side.

The orbital is separated from the lateral surface. The anteroinferior or maxillary border is rough and articulates with the upper jaw; its middle extremity is pointed and is above the infraorbital foramen, near the orbital margin, giving rise to a part of the upper elevator.

The posterosuperior or temporal-curved border is continuous above the posterior edge of the frontal process and below the upper edge of the zygomatic arch, which attaches to the temporal fascia.

A little below the fronto-zygomatic suture, this edge has a small rounded projection, called the marginal tubercle, which can be easily felt through the skin. The posteroinferior or zygomatic edge allows attachment by its rough edge to the masseter muscle.

The posteromedial border is serrated for the joint with the greater wing of the anterior sphenoid and the orbital surface of the lower jaw. There is usually a short, concave and non-articular part between these two toothed parts, which forms the lateral limit of the inferior orbital fissure.

This non-articulating part is sometimes absent. The fissure is completed by the maxilla and sphenoid bone junction or by the interposition of a small sutural bone in the angular interval between them.

The frontal process is thick and serrated (closed form), articulated above with the zygomatic process of the frontal bone and behind the sphenoid’s greater wing.

In its orbital aspect, just inside the orbital opening and approximately 11 mm below the fronto-zygomatic suture, there is a tubercle of variable size and shape.

The temporal process is directed backward and ends in an oblique and serrated margin that is articulated with the zygomatic process of the temporal bone and helps to form the zygomatic arch.

The zygomatic bone is ossified from a center, which appears around the eighth week of fetal life. The bone is sometimes divided by a horizontal suture in a more prominent upper-division and a smaller lower one.

Function

In addition to supporting the lateral wall and floor of the orbit, the zygomatic bone also articulates with (i.e., connects) other facial bones.

These include the maxilla (the upper jaw that contains the upper teeth), the frontal bone (the “browbone” that is part of the brain box and the orbit), the sphenoid bone (located “below” or behind the arch), zygomatic) and, of course, the temporal bone, with which it forms the zygomatic angle.

The zygomatic arch supports the primary maxillary muscle, the masseter, which is necessary both for biting and for chewing food and speech. Several other facial muscles are attached to the zygomatic bone as well.

Medical considerations

In facial fractures, the fracture line commonly passes through the zygomatic and sphenoid bones and continues to the junction between the zygomatic and frontal bones.

These fractures are called complex zygomatic fractures and can be complex to repair surgically due to the possibility of damage to the eye.

People of Asian descent usually have a prominent zygoma. Occasionally, Asians may request elective cosmetic surgery to reduce the cheekbone size.

Evolution of the zygomatic arch

In comparative anatomy, the zygomatic bone is also called jugal bone, which is found in all tetrapods (amphibians, reptiles, birds, and mammals).

In the ancestors of mammals, the synapsid reptiles, there was a single opening in the skull behind the eye socket. The jugal bone (zygomatic) extends from the lower part of the eye socket to the bottom of this opening.

Around the time when the first mammals evolved, the vertical separation between this opening and the orbit disappeared, leaving the zygomatic arch formed by the zygomatic bone and the temporal bone.

A vertical connection between the zygomatic and frontal bone is again present in humans, but the zygomatic arch remains.