Zygomatic bone

In the human skull, the zygomatic bone (cheekbone, malar bone) is a paired bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. The zygomatic is homologous to the jugal bone of other tetrapods. It is situated at the upper and lateral part of the face and forms the prominence of the cheek, part of the lateral wall and floor of the orbit, and parts of the temporal and infratemporal fossa. It presents a malar and a temporal surface; four processes, the frontosphenoidal, orbital, maxillary, and temporal; and four borders.

Etymology

The term zygomatic derives from the Greek Ζυγόμα zygoma meaning "yoke". The zygomatic bone is occasionally referred to as the zygoma, but this term may also refer to the zygomatic arch or the zygomatic process.

Human anatomy

Surfaces

The malar surface is convex and perforated near its center by a small aperture, the zygomaticofacial foramen, for the passage of the zygomaticofacial nerve and vessels; below this foramen is a slight elevation, which gives origin to the Zygomaticus.

The temporal surface, directed posteriorly and medially, is concave, presenting medially a rough, triangular area, for articulation with the maxilla (articular surface), and laterally a smooth, concave surface, the upper part of which forms the anterior boundary of the temporal fossa, the lower a part of the infratemporal fossa. Near the center of this surface is the zygomaticotemporal foramen for the transmission of the zygomaticotemporal nerve.

Process

The zygomatic process is a protrusion from the rest of the skull, like the bumper of a car. Most of it belongs to the zygomatic bone, but there are other bones contributing to it too, namely the frontal bone, maxilla and temporal bone.

Borders

The antero-superior or orbital border is smooth, concave, and forms a considerable part of the circumference of the orbit.

The antero-inferior or maxillary border is rough, and bevelled at the expense of its inner table, to articulate with the maxilla; near the orbital margin it gives origin to the Quadratus labii superioris.

The postero-superior or temporal border, curved like an italic letter f, is continuous above with the commencement of the temporal line, and below with the upper border of the zygomatic arch; the temporal fascia is attached to it.

The postero-inferior or zygomatic border affords attachment by its rough edge to the Masseter.

Ossification

The zygomatic bone is generally described as ossifying from three centers — one for the malar and two for the orbital portion; these appear about the eighth week and fuse about the fifth month of fetal life.

Mall describes it as being ossified from one center which appears just beneath and to the lateral side of the orbit.

After birth, the bone is sometimes divided by a horizontal suture into an upper larger, and a lower smaller division.

In some quadrumana the zygomatic bone consists of two parts, an orbital and a malar.

Articulations

The zygomatic articulates with four bones: the frontal, sphenoidal, temporal, and maxilla.

In other animals

In non-mammalian vertebrates, the zygomatic bone is referred to as the jugal bone, since these animals have no zygomatic arch. In coelacanths and early tetrapods the bone is relatively large. Here, it is a plate-like bone forming the lower margin of the orbit and much of the side of the face. In ray-finned fishes it is reduced or absent, and the entire cheek region is generally small. The bone is also absent in living amphibians.^[1]

With the exception of turtles, the jugal bone in reptiles forms a relatively narrow bar separating the orbit from the inferior temporal fenestra, of which it may also form the lower boundary. The bone is similarly reduced in birds. In mammals, it takes on broadly the form seen in humans, with the bar between the orbit and fenestra vanishing entirely, and only the lower boundary of the fenestra remaining, as the zygomatic arch.^[1]

Additional images

See also

• Bone terminology
• Cheek
• Terms for anatomical location

References

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

External links

• Roche Lexicon - illustrated navigator, at Elsevier 34256.000-1