Muscle architecture or the shape of skeletal muscles helps to shape their external appearance and determines their range of movement. Spiral muscles, as found in the trapezius muscle of the back, produce a twisting action at joints, Triangular bundles of muscle fibers, which appear fan-shaped, are arranged at an angle to the line of pull, as for example the temporalis muscles involved in chewing. Strap-like muscles, such as the sartorius of the leg and the sternohyoid of the neck, have parallel arrangement of fiber bundles. They are capable of both subtle and powerful contractions. Multipennate muscles, like the deltoid of the arm, are composed of many short bundles of fibers. Despite a limited range of shortening, these muscles are powerful in their actions.