The mouse pericardium: it allows passage of particulate matter from the pleural to the pericardial cavity.

Frog erythrocytes injected into the pleural cavity of mice reached the pericardial cavity. Pericardial pores that connect the two cavities were the routes of the migration. As soon as 5 minutes after injection, frog erythrocytes were surrounded and phagocytosed by attached macrophages in milky spots facing the pericardial cavity. The pericardial pores may function in an allied self-defense mechanism between the pleural and pericardial cavities in this species.