A 58-year-old man with newly diagnosed atrial fibrillation presents to the emergency department with acute left upper quadrant pain radiating to the left shoulder, fever, and leukocytosis. Contrast-enhanced CT abdomen shows a wedge-shaped hypodense lesion in the spleen with its base at the capsule and apex pointing toward the hilum, with no enhancement on the arterial phase. The structure marked **A** in the diagram represents this infarct. Which of the following best explains why splenic infarction characteristically assumes this wedge-shaped configuration with the base at the capsule?