342.A 28-year-old woman comes into the emergency room exhibiting
dyspnea and mild cyanosis, but nosigns of trauma. Her chest x-ray is
shown below. The most obvious abnormal finding in the inspiratory pos-
teroanterior chest x-ray of this patient (viewed in the anatomic position) is
a left pneumothorax (collapsed lung) as indicated by the dark appearance
of the left lung and the shifting of the heart to the right. Which of the fol-
lowing structures is indicated by the arrow?
464 Anatomy, Histology, and Cell Biology
a. Bilateral expansion of the pleural cavities above the first rib
b. Grossly enlarged heart
c. Aortic arch
d. Pulmonary trunk
e. Left ventricle