Suboccipital muscles refers to the muscles located below the occipital bone

Occipital bone

The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...

. The muscles are named: Rectus capitis posterior major, Rectus capitis posterior minor, Obliquus capitis inferior, and Obliquus capitis superior. There is also a Suboccipital triangle

Suboccipital triangle

The suboccipital triangle is a region of the neck bounded by the following three muscles of the suboccipital group of muscles:* Rectus capitis posterior major - above and medially* Obliquus capitis superior - above and laterally...

.These are four muscles on the underside of the occipital bone, the two oblique muscles and the two rectus muscles, collectively these are called the suboccipital muscles.
The rectus capitis minor muscle goes from the middle of the posterior arch of the atlas to the occipit. The rectus capitus major goes from the spinous process of the atlas to the occipital bone, lateral to the site of insertion of the rectus capitis minor. The two oblique, or obliquus capitis muscles, the inferior and the much smaller the superior. The inferior oblique muscle goes from the spine of the axis vertebra to the transverse process of the atlas .The superior oblique, goes from the transverse process of the atlas to the occiput.
The action of subcapital muscles is to extend the head and to rotate it toward the same side