The projecting back part of the skull is called the occiput and the space just below it down to the axis is defined as the suboccipital region. This region contains parts of 3 bones, 4 muscles, 3 nerves, 1 major artery (and 2 lesser ones), and a venous plexus. The key feature of the region is the suboccipital triangle.

1. SKELETAL FOUNDATION:

A. The area of the occipital bone below the inferior nuchal line

B. The posterior arch and transverse processes of the atlas

C. The laminae and spinous process of the axis

2. SUBOCCIPITAL MUSCLES: Of the 2 straight and 2 oblique suboccipital muscles only the rectus capitis posterior minor does NOT form a boundary of the triangle. The primary function of these muscles is to stabilize the atlanto-occipital and atlanto-axial joints though they may assist in extension and rotation.

A. Rectus capitis posterior minor (the short spino-occipital muscle)

B. Rectus capitis posterior major (the long spino-occipital muscle)

C. Obliquus capitis inferior (the spino-transverse muscle)

D. Obliquus capitis superior (the transverso-occipital muscle)

3. FLOOR OF THE TRIANGLE:

A. The posterior atlanto-occipital membrane

B. The posterior arch of the atlas which bisects the triangle into superior and inferior divisions

4. ROOF OF THE TRIANGLE --- the semispinalis capitis

5. NERVES (all dorsal primary rami):

A. C1 -- the suboccipital nerve which lies within the triangle and supplies all 4 suboccipital muscles

B. C2 -- the greater occipital nerve which supplies the splenius capitis and semispinalis capitis and skin on the back of the scalp

C. C3 -- the third occipital nerve which also supplies skin on the back of the scalp

6. ARTERIES:

A. The vertebral artery exits from the transverse foramen of the atlas and runs transversely on the posterior arch before disappearing through the posterior atlanto-occipital membrane en route to the brain

B. Anastomotic branches of the deep cervical and occipital arteries