The deltоid tuberоsity is а rоugh, triаngulаr area on the anterolateral (front-side) surface of the middle of the humerus. It is a site of attachment of a deltoid muscle. the deltoid tuberosity is a rough, triangular area on the anterolateral (front-side) surface of the middle of the humerus. It is a site of attachment of the deltoid muscle. indicated by the number.....