514 



THE BLOOD-VASCULAR SYSTEM 



caval orifice. Also that the caval opening and the fossal ovahs (containnig the foetal foramen 

 ovale) are in hearts well hardened before removal, situated in a distmct diverticulum to the 

 left of the remainder of the atrium. Between this diverticulum and the atrium proper, the 

 caval valve and the limbus fossa; ovalis form a prominent flange, better marked in the foetus 

 than the adult. Opening into the right atrium, particularly upon the septal and right lateral 

 walls, are numerous /oromina venarum minimarum (Thebesii). 



The left atrium [a. sinistrum] (fig. 425) is to the left and somewhat posterior 

 to the right. It is behind the root of the aorta and its auricle is to the left of the 



Fig. 428. — Interior of the Right Atrium and Ventricle. 

 The atrio-ventricular bundle is dissected out. 



• Left common carotid artery 





■ Innominate artery 



Aortic arch ' 



Vena cava superior 



Right pulmonary 

 artery 



Reflexion of pericardium 

 y?" * . ■ Pulmonary artery 



Ascending aorta 



Left pulmonary valve 



) 



Valvula vena; 



Vena cava inferior 



Part of posterior tricuspid cusp Posterior papillary muscles 



pulmonary root. Opening into it posteriorly on the right and left sides, re- (i 

 spectively, are the right and loft upper and lower pulmonary veins. The valvula 1 

 foraminis ovaHs forms a more or k'ss distinct crescentic ridge on the septal wall 

 (fig. 425). This may not l)o attacluul to the limbus fossiB ovalis, in which case 

 there is a communication bcjtwecn the two atria. Absence of lateral adhesion 

 between the two septa atriorum docs not nccM'ssarily load to admixture of arterial 

 and venous blood during life. The loft ostium venosum (atrio-ventricular orifice) 



