Butterfly bone refers to the shoulders below, separated from the back on both sides of the symmetrical distribution of the two scapulae, located in the back of the thorax, is an inverted triangular flat bone, between the 2nd to 7th ribs, butterfly bone is very obvious in the thinner people. When the two upper limbs open and close, both sides of the thin scapula will also open and close, like a butterfly like flapping wings, so it is called the butterfly bone. The scapula belongs to the upper limb band bone, connecting the shoulder joint and the ribs of the thorax, without direct joints, playing the role of supporting the upper arm, upper limb. The front of the scapula is slightly concave, and the back of the scapula has an outwardly upward high ridge called the scapular ridge, the lateral end of which is called the acromion, which is the highest point of the shoulder.