Obliquus capitis superior muscle

The obliquus capitis superior muscle is a small muscle in the upper back part of the neck. It is one of the suboccipital muscles. It attaches inferiorly at the transverse process of the atlas (first cervical vertebra); it attaches superiorly at the external surface of the occipital bone. The muscle is innervated by the suboccipital nerve (the posterior ramus of the first cervical spinal nerve).

It acts at the atlanto-occipital joint to extend the head and bend the head to the same side.

Anatomy
The obliquus capitis superior muscle is one of the suboccipital muscles. It forms the superolateral boundary of the suboccipital triangle. It extends superoposteriorly from its inferior attachment to its superior attachment, becoming wider superiorly.

Attachments
The muscle's inferior attachment is at the superior surface of the transverse process of the atlas (C1).  

Its superior attachment is onto the lateral portion of  the external surface of the occipital bone between the superior nuchal line and inferior nuchal line.   Its superior attachment is situated lateral to that of the semispinalis capitis muscle, and overlaps the attachment of the rectus capitis posterior major muscle.

Innervation
The muscle receives motor innervation from the suboccipital nerve (i.e. the posterior ramus of the cervical spinal nerve 1 (C1)).  

Actions/movements
The muscle extends and (ipsilaterally) laterally flexes the head.