In human anatomy, the trapezius (/trəˈpiːzi.əs/) is either one of two large superficial muscles that extend longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula (shoulder blade). Its functions are to move the scapulae and support the arm.he trapezius muscle resembles a trapezium (trapezoid in American English), or diamond-shaped quadrilateral. The word spinotrapezius refers to the human trapezius, although it is not commonly used in modern texts.