The area below the human chin is a complex region with specific anatomical names and underlying structures. Understanding its components provides insight into its function and common visual characteristics. This region plays an important role in the overall structure and movement of the head and neck.
The Chin’s Names
The term “chin” commonly refers to the forward-most pointed part of the lower jaw. Anatomically, this projection of the lower jawbone is known as the “mentum” or “mental region,” derived from the Latin word for chin.
The broader area directly beneath the chin is called the “submental region” or “submental area,” indicating its location “sub” (under) the “mental” (chin) area. Anatomically, this region is defined as the “submental triangle,” an unpaired space in the midline of the neck.
Underlying Structures
Beneath the visible surface of the chin and submental region lies a network of bones, muscles, and other tissues. The most prominent bony structure contributing to the chin’s shape is the mandible, or lower jawbone. This is the largest and strongest bone in the face, and uniquely, it is the only bone in the skull capable of movement, which is essential for chewing and speaking.
Further down in the neck, a distinctive U-shaped bone called the hyoid bone is located between the chin and the thyroid cartilage. The hyoid bone is unique because it is the only bone in the human body that does not directly connect to any other bone. Instead, it is suspended in place by a complex arrangement of ligaments and muscles, playing a role in tongue movement, swallowing, and speech.
Several muscles contribute to the form and function of this area. The platysma is a broad, thin muscle that spreads across the neck, lying just beneath the skin and covering deeper structures. Deeper still, the mylohyoid muscles form the muscular floor of the submental region, while the anterior bellies of the digastric muscles define its lateral borders. Small submental lymph nodes are also situated within the submental triangle, forming part of the body’s immune system.
Common Visual Features
The appearance of the area under the chin varies due to genetics, age, and lifestyle factors. A common visual characteristic is the “double chin,” medically known as submental fullness. This occurs when excess fat accumulates beneath the chin, softening the jawline’s definition.
Submental fat can reside in different layers, including superficial fat just under the skin and deeper fat positioned around the neck muscles. Factors such as weight gain, the natural aging process leading to reduced skin elasticity, and genetics can influence the presence and prominence of submental fullness. The overall definition of the jawline is primarily determined by the underlying bone structure of the mandible. However, the visibility of this definition can be affected by the amount of overlying fat and the laxity of the skin.