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 Hes above the right ventricle. 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 



Anterior vena cava 



Orifice of vena azygos 



Pulmonary veins 



Right auricle 



{appendix) 



Right atrium 

 {septal irall) 



Conus 

 arteri- 

 J^osus 



Orifice of 

 coronary sinics 



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 veatricle wa.s in diastole, r, Intervenous crest; v, v, tricuspid valve; p, p, papillary muscles; m, m, 



moderator bands. Arrow points into origin of pulmonary artery. 



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

 pulmonary artery. 



There are five chief openings in the right atrium. The opening of the anterior 

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

 opening of the posterior vena cava (Ostium venee 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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