In thehuman skull, thezygomatic bone (fromAncient Greek:ζῠγόν,romanized: zugón,lit. 'yoke'), also calledcheekbone ormalar bone, is a pairedirregular bone, situated at the upper and lateral part of the face and forming part of the lateral wall and floor of theorbit, of thetemporal fossa and theinfratemporal fossa. It presents a malar and a temporal surface; fourprocesses (the frontosphenoidal, orbital, maxillary, and temporal), and four borders.
The termzygomatic derives from theAncient GreekΖυγόμα,zygoma, meaning "yoke". The zygomatic bone is occasionally referred to as thezygoma, but this term may also refer to thezygomatic arch.
Themalar surface is convex and perforated near its center by a small aperture, thezygomaticofacial foramen, for the passage of the zygomaticofacial nerve and vessels; below this foramen is a slight elevation, which gives origin to thezygomaticus muscle.
Thetemporal 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 thetemporal fossa, the lower a part of the infratemporal fossa. Near the center of this surface is the zygomaticotemporal foramen for the transmission of thezygomaticotemporal nerve.
Theorbital surface forms the lateral part and some of the inferior part of the bony orbit. Thezygomatic nerve passes through the zygomatic-orbital foramen on this surface. The lateral palpebral ligament attaches to a small protuberance called the orbital tubercle.
Each zygomatic bone is diamond-shaped and composed of three processes with similarly named associated bony articulations: frontal, temporal, and maxillary. Each process of the zygomatic bone forms important structures of the skull.
The orbital surface of the frontal process of the zygomatic bone forms the anterior lateral orbital wall, with usually a small paired foramen, the zygomaticofacial foramen opening on its lateral surface. The temporal process of the zygomatic bone forms the zygomatic arch along with the zygomatic process of the temporal bone, with a paired zygomaticotemporal foramen present on the medial deep surface of the bone. The orbital surface of the maxillary process of the zygomatic bone forms a part of the infraorbital rim and a small part of the anterior part of the lateral orbital wall.[1]
Theorbital process is a thick, strong plate, projecting backward and medialward from the orbital margin. Itsantero-medial surface forms, by its junction with the orbital surface of themaxilla and with the great wing of thesphenoid, part of the floor and lateral wall of the orbit. On it are seen the orifices of two canals, thezygomatico-orbital foramina; one of these canals opens into thetemporal fossa, the other on the malar surface of the bone; the former transmits thezygomaticotemporal, the latter thezygomaticofacial nerve.
Itspostero-lateral surface, smooth and convex, forms parts of the temporal and infratemporal fossae.
Itsanterior margin, smooth and rounded, is part of the circumference of the orbit.
Itssuperiormargin, rough, and directed horizontally, articulates with the frontal bone behind the zygomatic process.
Itsposterior margin is serrated for articulation, with the great wing of the sphenoid and the orbital surface of the maxilla.
At the angle of junction of the sphenoidal and maxillary portions, a short, concave, non-articular part is generally seen; this forms the anterior boundary of the inferior orbital fissure: occasionally, this non-articular part is absent, the fissure then being completed by the junction of the maxilla and sphenoid, or by the interposition of a small sutural bone in the angular interval between them.
Theantero-superior ororbital border is smooth, concave, and forms a considerable part of the circumference of the orbit.
Theantero-inferior ormaxillary 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 thequadratus labii superioris.
Thepostero-superior ortemporal border, curved like an italic letterf, is continuous above with the commencement of the temporal line, and below with the upper border of thezygomatic arch; the temporal fascia is attached to it.
Thepostero-inferior orzygomatic border affords attachment by its rough edge to themasseter.
The zygomatic bone is generally described asossifying 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 somequadrumana the zygomatic bone consisted of two parts, an orbital and a malar.
Zygomatic arches, also known as high cheek bones, are consideredphysically attractive in some cultures, in both males and females.[2][3]
AncientChinese sculptures of goddesses typically have a "broad forehead, raisedeyebrows, high cheekbones, and large, sensuous mouth".[4] Similarly, many depictions of Qin warriors in theTerracotta Army are depicted with "broadforeheads, high cheekbones, large eyes, thick eyebrows, and stiffbeards."[4]
Diagram showing homologous bones of the skulls of aMonitor lizard and aCrocodile. Jugal bone labelledJu, in pale green, at centre left.
This jugal bone from anEdmontosaurus is over three feet (1 meter) long
In non-mammalian vertebrates, the zygomatic bone is referred to as thejugal bone, since these animals have no zygomatic arch. It is found in mostreptiles,amphibians, andbirds. It is connected to thequadratojugal andmaxilla, as well as other bones, which may vary by species.
This bone is considered key in the determination of general traits of the skull, as in the case of creatures, such asdinosaurs inpaleontology, whose entire skull has not been found. Incoelacanths and earlytetrapods 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. Inray-finned fishes it is reduced or absent, and the entire cheek region is generally small. The bone is also absent in livingamphibians.[6]
With the exception ofturtles, the jugal bone inreptiles forms a relatively narrow bar separating the orbit from the inferiortemporal fenestra, of which it may also form the lower boundary. The bone is similarly reduced inbirds. 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.[6]
^abRomer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 217–241.ISBN0-03-910284-X.
