It is a closed sac having two layers: the visceral layer (epicardium), immediately surrounding the heart, and the outer parietal layer, forming the sac, composed of strong fibrous tissue, the fibrous pericardium, lined with a serous membrane, the serous pericardium. Synonym(s): heart sac, theca cordis.
The right and left cavernous sinuses are interconnected by the anterior and posterior intercavernous sinuses. Tributaries of the cavernous sinus include the superior ophthalmic, superficial middle cerebral, and inferior cerebral veins and the sphenoparietal sinus.
All 3 internodal pathways emerge from the sinus node. Anterior pathway plus interatrial pathway are indicated with dots; division of that pathway into the interatrial direction is marked with the lower right black arrow, and the branch forming the anterior internodal pathway is marked by the upper right black arrow.