The lateral (temporomandibular) ligament is the primary structure that restricts excessive lateral movement of the mandible. This ligament is a thickened band of the fibrous capsule of the temporomandibular joint (TMJ) and runs from the articular tubercle of the temporal bone to the neck of the mandible. Its main function is to strengthen the joint laterally and prevent excessive sideways displacement, thereby stabilizing the mandible during movements such as chewing and speaking.

In contrast, the stylomandibular ligament and sphenomandibular ligament serve more as passive supports limiting extreme movements but do not primarily control lateral displacement. The capsular ligament encloses the TMJ and contains synovial fluid but provides more general support rather than specific restriction of lateral movement.

Therefore, the lateral (temporomandibular) ligament is essential for maintaining joint stability during lateral excursions of the mandible.

Key points:
- Lateral ligament strengthens the TMJ laterally
- Prevents excessive lateral (side-to-side) movements of the mandible
- Originates from articular tubercle to mandibular neck
- Other ligaments support the joint but do not primarily restrict lateral displacement

Reference: Gray's Anatomy, 41st Edition, Volume 1, Chapter 46 – Temporomandibular Joint