What Is the Sphenomandibularis Muscle? A Scientific Debate

The sphenomandibularis is a small muscle deep within the face and is one of the muscles of mastication, the group responsible for moving the lower jaw. Its identification is relatively recent, first described by researchers in the mid-1990s. This discovery challenged the long-held belief that the body’s musculature was fully mapped.

Anatomical Location and Structure

The sphenomandibularis muscle is situated deep in the infratemporal fossa, an area behind the cheekbone and below the temple. It originates from a part of the skull base known as the sphenoid bone, specifically from a surface on the greater wing of this bone located behind the eye socket. From its origin, the muscle fibers travel downwards to attach to the lower jaw, or mandible.

Its specific insertion point is on the inner surface of the mandible, near the junction where the vertical part (ramus) meets the horizontal part (body). This attachment site, called the internal oblique line, was previously considered just a radiographic landmark with little clinical importance. The muscle itself is relatively small, measuring about one-and-a-half inches long and three-quarters of an inch wide. Its deep placement makes it difficult to feel from the outside and distinguishes it from larger, more superficial chewing muscles like the masseter.

Proposed Role in Jaw Movement

The primary function attributed to the sphenomandibularis is to assist in elevating the mandible (closing the jaw) for biting and grinding food. When the muscle contracts, it pulls upward on the mandible, contributing to the powerful force needed for chewing. Its action is therefore synergistic with other, larger jaw-closing muscles such as the temporalis and masseter.

Beyond simply closing the jaw, it is also suggested to play a role in stabilizing the mandible during movement. The temporomandibular joint, which connects the jaw to the skull, allows for complex motions including side-to-side and forward-backward shifts. The sphenomandibularis may help guide and steady the jawbone during these actions, ensuring coordinated function while speaking or chewing.

The Debate Over Its Existence

The classification of the sphenomandibularis as a distinct muscle is a subject of ongoing scientific discussion. The original discovery was made when researchers used an unconventional dissection approach, accessing the anatomy from the front rather than the traditional side view. This new perspective revealed a bundle of muscle fibers that, according to the discoverers, had a unique origin and insertion point separate from its neighbors, leading them to propose it as a new muscle.

However, many anatomists and sources contend that the sphenomandibularis is not an independent muscle. The opposing viewpoint holds that these fibers are actually a deep, somewhat isolated part of the much larger temporalis muscle. The temporalis is a broad, fan-shaped muscle on the side of the head, and it is plausible that some of its deeper fibers could appear separate. The structure is not consistently listed in all anatomy textbooks, reflecting this lack of consensus.

Potential Clinical Significance

Regardless of its classification, the muscular tissue identified as the sphenomandibularis has clinical relevance for facial pain and jaw disorders. Dysfunction in this deep facial region can cause discomfort, including headaches that are felt behind the eye (retro-orbital) or in the temples. Because it is a jaw-elevating muscle, tension or overuse, such as from teeth grinding (bruxism), can lead to inflammation and pain.

This structure is of particular interest in diagnosing and treating Temporomandibular Disorders (TMD), conditions causing pain and dysfunction in the jaw joint and its controlling muscles. Inflammation or the development of trigger points in this muscle can mimic or contribute to TMD symptoms, such as jaw clicking, limited opening, and chronic facial pain. For clinicians, recognizing that this deep muscle can be a source of pain is useful for accurate diagnosis, especially when symptoms do not respond to treatments targeting the larger masticatory muscles.