azygos vein: one of a system of veins that drain the thoracic and abdominal walls; arises as a continuation of the right ascending lumbar vein and terminates in the superior vena cava
entity: that which is perceived or known or inferred to have its own distinct existence (living or nonliving)
sternocleidomastoid: one of two thick muscles running from the sternum and clavicle to the mastoid and occipital bone; turns head obliquely to the opposite side; when acting together they flex the neck and extend the head