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.
In birds and mammals the sinus venosus is formed in the embryo and subsequently (except in unkeeled birds) is completely incorporated in the wall of the right auricle, together with the sinus node; only in Monotremata are the sinoatrial valves preserved. (3) In a number of invertebrates, the same as venous lacunae.n the sinus venosus is found the sinus node (Remakâs ganglion), the center in which the primary impulses of heart contraction originate. In reptiles (except for Hatteria) the sinus venosus loses complete independence and enters, to one degree or another, into the structure of the right auricle.