The forehead, known anatomically as the frons, is a distinct region of the head that forms the upper third of the face. While its location seems obvious, the exact boundaries where the forehead begins and ends are not arbitrary lines but are precisely defined by underlying bony and muscular landmarks. These specific anatomical borders are universally recognized in medicine and anthropology to ensure accurate communication and surgical planning. Understanding these definitions requires moving beyond the simple visual appearance to examine the specific structures that separate the forehead from the scalp, the orbital region, and the temples.
Defining the Superior Border
The superior limit of the forehead marks its transition into the hair-bearing scalp, which is anatomically termed the capillitium. This boundary is commonly understood as the anterior hairline, though this is a soft tissue landmark that can be highly variable among individuals or unstable due to aging or hair loss. The true anatomical definition lies in the complex structure of the muscles and connective tissue beneath the skin.
The superior border is formed by the junction where the Frontalis muscle ends and blends into a wide, dense sheet of fibrous tissue called the Galea Aponeurotica. The Frontalis muscle, which is responsible for raising the eyebrows, has no direct bony attachment in this area. Instead, its fibers continue upward and become contiguous with the Galea Aponeurotica, which covers the top of the skull. This muscular and fascial merger essentially defines the functional upper extent of the forehead. The forehead officially begins where the muscle belly of the Frontalis starts its downward course toward the eyebrows.
Defining the Inferior Border
The inferior boundary of the forehead separates it from the orbital and nasal regions. This line is clearly established by the prominent bony ridge located directly above the eyes. The border extends laterally along the Supraorbital Margins, which are the upper edges of the eye sockets formed by the frontal bone.
Near the center, between the eyebrows, the inferior boundary includes the Glabella, a smooth, slightly depressed area of bone. Directly beneath the skin in this region are the Superciliary Arches, or brow ridges, which are more pronounced in males. The skin overlying the Glabella and the Supraorbital Margins is considered the lowermost part of the forehead. The Supraorbital Margin is also significant because the Supraorbital and Supratrochlear nerves and vessels pass through a notch or foramen in this bone, supplying sensation to the forehead skin. The center point of the inferior border is often referenced using the Nasion, the bony landmark where the frontal bone meets the nasal bones.
Defining the Lateral Borders
The side boundaries of the forehead differentiate it from the temporal region, often referred to as the temples. This lateral separation follows a distinct bony line that curves backward from the area of the eye socket. The line is defined by the Temporal Lines on the frontal bone, specifically the Superior Temporal Line.
This bony ridge sweeps upward and backward from the Zygomatic Process of the frontal bone, which articulates with the cheekbone. The Superior Temporal Line serves as the attachment point for the Temporal Fascia, a robust layer of tissue that covers the Temporalis muscle beneath it. Because the forehead’s skin and musculature are superficial to this fascia, the Temporal Line acts as a natural division, distinguishing the smooth, central forehead region from the side of the head. The lateral edge of the Frontalis muscle often thins out and does not extend all the way to this bony line, confirming the Superior Temporal Line as the accepted lateral limit of the forehead structure.
Why Precise Definitions Matter
Defining the borders of the forehead is foundational for several medical and scientific disciplines. In reconstructive and plastic surgery, these fixed anatomical boundaries are used to plan procedures like brow lifts, hairline lowering, and the placement of soft tissue fillers or neuromodulators. Surgeons must have a precise understanding of the location of the Supraorbital and Supratrochlear neurovascular bundles, which exit near the inferior border, to avoid nerve damage and excessive bleeding.
In forensic anthropology and cephalometry, measurements taken between landmarks like the Glabella and the superior border are used to determine skull proportions for identification and comparative analysis. For the general public, knowing these lines helps to understand why cosmetic treatments need to be administered with high accuracy. The anatomical map serves as a safety guide, ensuring that procedures are performed in the correct tissue layers and away from vulnerable structures, such as the frontal branch of the facial nerve, which supplies motor function to the Frontalis muscle.