1. Suboccipital triangle

• Is bound medially by the rectus capitis posterior major muscle, laterally by the obliquus
• capitis superior muscle, and inferiorly by the obliquus capitis inferior muscle.
• Has a roof formed by the semispinalis capitis and longissimus capitis.
• Has a floor formed by the posterior arch of the atlas and posterior atlanto-occipital membrane.
• Contains the vertebral artery and suboccipital nerve and vessels.
  

2. Suboccipital muscles

Muscle - Rectus capitis posterior major
Origin - Spine of axis
Insertion - Lateral portion of inferior nuchal line
Nerve - Suboccipital
Action - Extends, rotates, and flexes head laterally

Muscle - Rectus capitis posterior minor
Origin - Posterior tubercle of atlas
Insertion - Occipital bone below inferior nuchal line
Nerve - Suboccipital
Action - Extends and flexes head laterally

Muscle - Obliquus capitis superior
Origin - Transverse process of atlas
Insertion - Occipital bone above inferior nuchal line
Nerve - Suboccipital
Action - Extends, rotates, and flexes head laterally

Muscle - Obliquus capitis inferior
Origin - Spine of axis
Insertion - Transverse process of atlas
Nerve - Suboccipital
Action - Extends and rotates head laterally

3. Suboccipital nerve

• Is derived from the dorsal ramus of C1 and emerges between the vertebral artery above and the posterior arch of the atlas below.
• Supplies the muscles of the suboccipital triangle and semispinalis capitis.
• Contains skeletal motor fibers and no cutaneous sensory fibers, but occasionally has a cutaneous branch.

• Arises from the subclavian artery and ascends through the transverse foramina of the upper six cervical vertebrae.
• Winds behind the lateral mass of the atlas, runs in a groove on the superior surface of the posterior arch of the atlas, pierces the dura mater to enter the vertebral canal, and ascends into the cranial cavity through the foramen magnum.
• Gives off an anterior spinal and two posterior spinal arteries.

• Are formed in the suboccipital triangle by union of tributaries from the venous plexus around the foramen magnum, the suboccipital venous plexus, the intervertebral veins, and internal and the external vertebral venous plexus.
• Do not emerge from the cranial cavity with the vertebral artery through the foramen magnum, but they enter the transverse foramen of the atlas and descend through the next five successive foramina, emptying into the brachiocephalic vein. The small accessory vertebral veins arise from the plexus, traverse the seventh cervical transverse foramina, and end in thebrachiocephalic vein.

Atlanto-occipital joint

• Is a condylar synovial joint that occurs between the superior articular facets of the atlas and the occipital condyles.
• Is involved primarily in flexion, extension , and lateral flexion of the head.

Atlantoaxial joints

• Are synovial joints consisting of two lateral plane joints , which are between articular facets of the atlas and axis, and one median pivot joint between the dens of the axis and the anterior arch of the atlas.
• Are involved in rotation of the atlas and head as a unit on the axis.

Cruciform ligament

1. Transverse ligament

• Runs between the lateral masses of the atlas, arching over the dens of the axis.

2. Longitudinal ligament

• Extends from the dens of the axis to the anterior aspect of the foramen magnum and tothe body of the axis.

Apical ligament

• Extends from the apex of the dens to the anterior aspect of the foramen magnum (of the occipital bone).

Alar ligament
Extends from the apex of the dens to the tubercle on the medial side of the occipital condyle.

Tectorial membrane

• Is an upward extension of the posterior longitudinal ligament from the body of the axis to the basilar part of the occipital bone anterior to the foramen magnum.
• Covers the posterior surface of the dens and the apical, alar, and cruciform ligaments.