The surface marking of the arch of aoa is as follows

ARCH OF AOA It lies behind the lower half of the manubrium sterni.Its upper convex border is marked by a line which begins at the right end of the sternal angle,arches upwards and to the left through the centre of the manubrium and ends at the sternal end of the left second costal cailage.Note that the beginning and end of the arches are at the same level.When marked on the surface as descried above the arch looks much smaller than it actually is because of foreshoening. BD CHAURASIA 'S HUMAN ANATOMY VOL.1,FIFTH EDITION