<s>[INST] context: Right border of the mediastinal shadow (chiefly produced due to the hea and the vessels entering and leaving it) is formed from above downwards by the right brachiocephalic vein, superior vena cava, right atrium and the inferior vena cavaThe Base of the HeaThe base is located posteriorly and is formed mainly by the left atrium.It lies opposite T5 to TS (supine position) and T6 to T9 veebrae (erect position) and faces superiorly, posteriorly and towards the right shoulder.The base or posterior aspect of the hea is quadrilateral in shape and it is from its most superior pa from which the ascending aoa and pulmonary trunk emerge, and into which the superior vena cava enters.The base is separated from the diaphragmatic surface of the hea by the posterior pa of the coronary groove (L. sulcus).The Apex of the HeaThis blunt apex is formed from by the left ventricle, which points inferolaterally.The apex is located posterior to the left 5th intercostal space in adults, 7 to 9 cm from the median plane, and just left of the midclavicular line.The apex beat is an impulse impaed by the hear; it is its point of maximal pulsation or the lowest, most lateral point at which pulsation can be felt.The Sternocostal (Anterior) Surface of the HeaThis surface of the hea is mainly formed by the right ventricle and is visible in PA radiographs of the thorax.The Diaphragmatic (Inferior) Surface of the HeaThe surface of the hea is usually horizontal or slightly concave.It is formed by both ventricles, mainly the left one.The posterior interventricular sulcus divides this surface into a right 1/3 and a left 2/3.The Pulmonary (Left) Surface of the HeaThis surface of the hea is mainly formed by the left ventricle and occupies the cardiac notch of the left lung.Radiological Anatomy of the HeaIn PA radiographs of the thorax, the right border of the cardiovascular silhouette is formed by (superior to inferior): (1) the superior vena cava; (2) the right atrium; (3) the inferior vena cava.The left border of the cardiovascular silhouette is formed by: (1) the arch of the aoa, which produces a characteristic aoic knob; (2) the pulmonary trunk; (3) the left auricle; (4) the left ventricle. [/INST] question: Which of these does not form the right border of the hea on X-ray: | options: A: Right atrium B: Arch of aoa C: Superior vena cava D: Inferior vena cava | answer: B </s>