During head rotation to the contralateral side, the cephalic part of IJV is moved to the same direction. Accordingly, the investigators thought that the counter traction of the caudal part of IJV using the caudo-lateral traction of the ipsilateral arm might relieve the overlap caused from head rotation. Therefore, the investigators evaluated the effect of the caudo-lateral traction of the ipsilateral arm on the overlap between common CA and IJV in infants.