The cleidosternohyoid: a fifth infrahyoid muscle?

We describe a cleidosternohyoid muscle found bilaterally during routine dissection of a cadaver (92 year-old male of Irish descent). On the right side, the muscle originated from the clavicle with a cleidohyoid muscle. On the left side, the muscle originated from the clavicle and accompanied the inferior belly of an omohyoid muscle. On both sides the muscle inserted into the sternohyoid muscle. Since the muscle variant courses with a cleidohyoid on the right and the inferior belly of an omohyoid on the left, it is best described as a distinct fifth infrahyoid muscle rather than an accessory infrahyoid muscle. This is the first definitive case of a bilateral cleidosternohyoid reported in the literature.