The roof of the suboccipital triangle is formed by which muscle?

• A. Semispinalis Capitis
• B. Splenius Capitis
• C. Trapezius
• D. Rectus Capitis Posterior Major

Answer: (A)

In the tiny suboccipital region, the triangle is capped from above by a deep extensor muscle that covers the area like a lid. This muscle—semispinalis capitis—runs from the upper thoracic and lower cervical vertebrae to the occipital bone, lying over the triangle so it forms its roof. Beneath this roof lie important structures such as the vertebral artery and the suboccipital nerve.

The other muscles listed aren’t the roof: the rectus capitis posterior major helps form the medial boundary of the triangle, while splenius capitis and trapezius sit outside or at a different level and don’t cap the triangle.