This is a strong, fleshy muscle deeply seated on the side of the neck, in close apposition with the ligamentum nuchae, which divides the right from the left complexus. It extends from the back behind to the head in front, becoming narrower as it passes upwards.

Origin. - From the spinous processes of the 1st, 2nd, 3rd, and 4th dorsal vertebrae, from the transverse processes of the first six, and from the articular tubercles of all the cervical vertebrae.

Insertion. - Into the posterior part of the occipital bone*

Action. - Contracting alone, it would bend the neck to one side. Acting together with its fellow on the opposite side, it elevates and extends the head.