Zygoma

The zygoma (or zygomatic bone) is an important facial bone which forms the prominence of the cheek. It is roughly quadrangular in shape.

Gross anatomy

Zygoma has three surfaces:

• lateral or antero-lateral surface is convex and pierced at its orbital border by the zygomaticofacial foramen which houses the zygomaticofacial nerve and vessels
• temporal or postero-medial surface articulates with the maxilla, its smooth concave bony extent is seen posteriorly forming an incomplete wall of the infra-temporal fossa. The zygomaticotemporal foramen courses this surface near the base of frontal process
• orbital surface forms the antero-lateral part of the orbital floor and bears the zygomatico-orbital foramina, openings of the canals leading to zygomaticofacial and temporal foramina.

This bone has five borders:

• orbital or antero-superior border forms the inferolateral circumference of the orbital opening
• maxillary or antero-inferior border articulates with the maxilla, tapers just above the infraorbital foramen, zygomaticomaxillary suture exists between the maxillary margin of the zygomatic bone and the zygomatic process of the maxilla
• temporal or postero-superior border is of sinuous shape, convex above, concave below and continuous with the posterior border of the frontal process and upper border of the zygomatic arch
• postero-inferior border is roughened by the attachment of masseter muscle
• postero-medial border articulates with the greater wing of sphenoid above and orbital surface of maxilla below.

Zygomatic bone exhibits two processes:

• frontal process articulates with the frontal bone above and greater wing of sphenoid posteriorly terminates at the frontozygomatic suture.
• temporal process is directed backwards, has an oblique, serrated end articulating with the zygomatic process of temporal bone forming the zygomatic arch at the temporozygomatic suture.

Articulations

Zygoma articulates with the sphenoid's greater wing, orbital surface and lateral border of maxilla, temporal zygomatic process (completing the zygomatic arch) and frontal bone zygomatic process. 

Attachments

• lateral surface attaches the zygomaticus minor and major muscles
• postero-inferior border - masseter muscle
• frontal process' tubercle exhibits attachment of lateral palpebrae  ligamentligament, a suspensory ligament and part of the aponeurosis of levator palpebrae superioris
• maxillary border gives origin to a part of the levator labii superioris

Ossification

Zygoma ossifies from one centre appearing in fibrous tissue about the eighth week of life. Sometimes it may be divided by a horizontal suture into a larger upper and lower division.

Variants

• the zygomaticofacial foramen can often be double or sometimes be absent
• the tubercle attaching lateral palpebrae ligament from frontal process of zygoma is absent in 5-10% of skulls