The zygomatic arch is a prominent, paired structure of the human skull, often called the cheekbone arch. This bony bridge defines the width and contour of the midface. It acts as a protective barrier and an anchor point for muscles involved in chewing and jaw movement.
Visual and Tactile Location on the Skull
The zygomatic arch is easily felt on the side of the head. It begins at the most prominent part of the cheek and sweeps backward toward the ear. To locate it, place a finger just in front of the external ear canal, slightly above the earlobe.
Tracing this smooth, arc-like path forward, the bony ridge extends toward the eye socket and the center of the cheek. It is positioned just above the space where the lower jaw connects to the skull, and its outward curve largely determines the width of the cheeks.
Bony Components and Formation
Despite its appearance as a single structure, the zygomatic arch is actually a bridge formed by the meeting of two distinct bone processes. The front portion of the arch is the temporal process of the zygomatic bone, which extends backward from the cheekbone itself.
The rear portion of the arch is the zygomatic process of the temporal bone, which extends forward from the side of the skull, over the ear opening. These two bony projections join together at an oblique seam called the zygomaticotemporal suture. This fusion creates the complete arch that defines the lateral border of the face.
Primary Functions and Clinical Significance
The arch serves two main functional roles: providing a mechanical anchor for mastication muscles and offering protection for deeper structures. The lower border of the zygomatic arch serves as the origin point for the masseter muscle, a powerful muscle responsible for closing the jaw during chewing. The arch also spans a space beneath it, allowing the tendon of the temporalis muscle, another chewing muscle, to pass through to attach to the lower jaw.
Because of its exposed position on the side of the head, the zygomatic arch is vulnerable to trauma, and fractures are a common facial injury. A direct blow can cause the arch to fracture and potentially collapse inward. When this occurs, the depressed bone can impinge on the temporalis muscle, leading to trismus, which is the inability to fully open the mouth.
The integrity of the arch is important for both the aesthetics of facial contour and the mechanical function of the jaw. Restoring the form and function of the midface is the primary goal of treatment for these fractures. Additionally, nerves that supply sensation to the cheek and temple pass through foramina within the zygomatic bone, and a fracture can sometimes cause numbness in these areas.