The zygomatic bones are situated in the upper and lateral parts of the face. Each forms the prominence of the cheek, and contributes to the formation of the lateral wall and floor of the orbit and to the wails of the temporal and infratemporal fossae (fig. 394).

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

The lateral (malar) surface (figs. 394, 395), directed laterally and forwards, is convex and is pierced near its orbital border by the zygomaticofacial foramen (which is often double), for the passage of the zygomaticofacial nerve and vessels; below this foramen a slight elevation gives origin to the zygomaticus minor (zygomatic head of quadratus labii superioris), and more posteriorly the zygomaticus major (zygomaticus) takes origin. The temporal surface (fig. 396), directed medially and backwards, is concave, presenting anteriorly a roughened area for articulation with the maxilla, and posteriorly a smooth, concave area, which extends upwards on the posterior aspect of the frontal process to form the anterior boundary of the temporal fossa, and backwards on the medial aspect of the temporal process to form an incomplete lateral wall for the infratemporal fossa. The zygomaticotemporal foramen, for the transmission of the nerve of the same name, pierces this surface near the base of the frontal process. The orbital surface (fig. 396), smooth and concave, forms the anterolateral part of the floor and the adjoining part of the lateral wall of the orbit, extending upwards onto the medial aspect of the frontal process. It usually presents the orifices of two canals, termed the zygomatico-orbital foramina, one of which leads to the zygomaticofacial and the other to the zygomaticotemporal foramen.

The anterosuperior or orbital border is smooth and concave, and forms a considerable part of the circumference of the orbital opening, below and on the lateral side. It separates the orbital from the lateral surface. The antero-inferior or maxillary border is rough and articulates with the maxilla; its medial extremity is pointed and lies above the infraorbital foramen; near the orbital margin it gives origin to a part of the levator labii superioris (infra-orbital head of quadratus labii superioris). The posterosuperior or temporal border.curved like the italic letter �f�, is continuous above with the posterior border of the frontal process and below with the upper border of the zygomatic arch ; it gives attachment to the temporal fascia. A little below the frontozygomatic suture this border presents a small, rounded projection, termed the marginal tubercle, which can be felt easily through the skin. The postero-inferior or zygomatic border affords attachment by its rough edge to the masseter muscle.

Figure 394
Zygomatic bone in skull lateral view - Figure 394
The posteromedial border is serrated for articulation with the greater wing of the sphenoid above, and the orbital surface of the maxilla below. Between these two serrated portions there is usually a short, concave, non-articular part, which forms the lateral boundary of the inferior orbital fissure. This non-articular part is sometimes absent, and the fissure is then completed by the junction of the maxilla and the sphenoid bone, or by the interposition of a small sutural bone in the angular interval between them.

Figure 395
Zygomatic bone lateral view - Figure 395
Figure 396
Zygomatic bone medial view - Figure 396
The frontal process (frontosphenoidal process) is thick and serrated; it articulates above with the zygomatic process of the frontal bone and behind with the greater wing of the sphenoid. On its orbital aspect, just within the orbital opening and about 11 mm below the frontozygomatic suture, there is a tubercle of varying size and form, but present in 95 per cent. of skulls. The temporal process is directed backwards and ends in an oblique, serrated margin which articulates with the zygomatic process of the temporal bone, and helps to form the zygomatic arch.

Ossification.–The zygomatic bone is ossified from one centre, which appears about the eighth week of fetal life. The bone is sometimes divided by a horizontal suture, into an upper larger and a lower smaller division.

 


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