Which muscle forms the anterior border of the lateral cervical triangle?

• A. Sternocleidomastoid
• B. Trapezius
• C. Platysma
• D. Omohyoid

Answer: (A)

In the lateral (posterior) cervical triangle, the anterior border is formed by the sternocleidomastoid muscle. This muscle runs from the sternum and clavicle up to the mastoid process, and it clearly defines the front edge of the triangle, separating it from the neck’s anterior region. The trapezius forms the posterior boundary, not the front. The platysma is a superficial neck muscle over the superficial fascia and doesn’t define the triangle’s border. The omohyoid crosses the area and helps divide the posterior triangle into smaller subtriangles, but it isn’t the outer border.