THE RIGHT ATRIUM 



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The Right Atrium 



The right atrium (Atrium dextrum) or auricle forms the right-anterior part 



of the base of the heart, and lies above the right v(>ntricle. It consists of a sinus 



venosus, into which the veins open, and an auricle or auricular appendix. The 



latter is a conical diverticulum which curves around the right and anterior surfaces 



A Ilk rial' vena cava 



Orifice of vena azygos 



Pulmonary veins 



Right auricle 

 '^- (appendix) 



Right atrium 

 (septal wall) 



Orifice of 

 coronary sinus 



ChordoE tendinece 



Right ventri- 

 cle (septal 

 wall) 



Fig. 422. — Right Side of Heart of Horse Opened up by Removal of Greater Part of Right Wall. Organ 



Hardened in situ. 



The right ventricle was in diastole, r, Intervenous crest; v, v, tricuspid valve; p, p, papillary muscles; m, m, 



moderator bands, .^rrow points into origin of pulmonary artery. 



of the aorta, its blind end appearing on the left side in front of the origin of the 

 l)ulmonary artery. 



Th(>re are five chief openings in the right atrium. The opening of the anterior 

 vena cava (Ostium vena^ cavse cranialis) is in the upper and fore part. The 

 opening of the posterior vena cava (Ostium venae cava? caudalis) is at the lower 

 posterior part. Between the two the wall pouches upward somewhat, forming 

 what is sometimes termed the sinus venosus or sac of Lower. In the anterior part 

 -of this the vena azygos opens. The coronary sinus opens immediately below the 

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