====== RIGHT ATRIUM ======
  * Atrium dextrum - Right atrium
      * right atrium
        * External features
           * little ear or right auricle
              * covers the root of ascending aorta
              * partly overlaps the infundibulum of right ventricle
              * margins are notched and interior is sponge like
           * right border of atrium
              * along this border
                * shallow vertical groove
                  * passes from SVC to IVC
                    * sulcus terminalis ( corner sulcus )
                       * upper part contains SA node
                  * Caused by
                    * internal muscular ridge
                       * crista terminalis ( corner line )
           * right atrioventricular groove
              * separates
                * right atrium from the right ventricle
              * more or less vertical
                * lodges right coronary artery
                * small cardiac vein
      * Internal features
        * smooth posterior part or sinus venarum
          * most of tributaries except anterior cardiac vein drain in to it
            * superior venacava opens at upper end
            * inferior venacava opens at lower end
              * guarded by rudimentary valve
                * eustachian valve (gate )
                * in embryonic life
                   * directs IVC blood to left atrium
            * coronary sinus ( heart tank ) 
              * opens between
                * IVC opening and Right atrioventricular orifice
                * guarded by thebesian valve
            * venae cordis minimae ( small heart veins)
              * present in walls of all 4 chambers
                * open in to right atrium
          * derived from right horn of sinus venosus
          * intervenous tubercle of lower
            * posterior wall of atrium
        * rough anterior part or pectinate part 
          * derived from primitive artrial chamber
          * series of transverse muscular ridges
            * called musculi pectinati
        * interatrial septum
          * derived from septum primum and septum secundum
          * fossa ovalis
          * annulus ovalis or limbus fossa ovalis
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