Introduction of a New Classification of the Cleidooccipital Muscle

Abstract

The “cleidooccipital branches” are integral muscular branches of the sternocleidomastoid muscles (SCM), as well as the trapezius muscles, which construct the anterior and posterior borders of the posterior triangle of the neck, respectively. The term “cleidooccipital muscle”, in the literature, generally describes the accessory muscle, which is proximally attached to the middle portion of the clavicle, separate from the clavicular attachment of the SCM or trapezius muscle, and crosses the posterior triangle of the neck obliquely. With proximity to either the trapezius or the SCM, the accessory cleidooccipital muscles can be divided into posterior and anterior accessory cleidooccipital muscles, respectively. At present, most of the descriptions in the literature associated with the accessory cleidooccipital muscles concern the posterior accessory cleidooccipital muscles. The anterior accessory cleidooccipital muscles are mostly recognized as a proximal clavicular-head-sided supernumerary variation of the SCM. We propose a new classification of these muscles, with nomenclatures to help researchers to differentiate the cleidooccipital branches or muscles from one another. Introducing this classification, we hope that more clarity can be achieved when addressing the so-called “cleidooccipital muscle” in the future.