66 



THORAX 



the body and heart open into it. These two parts of the 

 cavity differ, however, not only in position and their relations 

 to the great veins, but also in the characters of their walls. 

 The whole of the interior of the atrium presents a polished 

 glossy appearance, due to the endocardial lining; but whilst the 

 wall of the venous sinus is smooth, the rest of the wall of the 

 atrium is rendered rugose by a large number of muscular ridges 



Aortt 



Crista 

 terminalis 



Superior vena cav: 

 f 



Upper right gjj 

 pulmonary veil 



Lower righ 



pulmonary 



vein 



Limbus fossae ovalis 



Fossa ovalis 



vena cava (Eustachian) Valve of the coronary sinus (Thebesian) 



FIG. 3'^. The Right Atrium. Part of the posterior wall and the whole 

 of the right lateral and anterior walls have been thrown anteriorly. 



which commence at the crista terminalis and run anteriorly to 

 the right margin of the atrium. These bundles, on account 

 of their somewhat parallel arrangement, are called the musculi 

 pectinati. 



The veins which open into the right atrium are the (i) 

 superior vena cava, (2) inferior vena cava, (3) coronary sinus, 

 (4) anterior cardiac veins, and (5) venae cordis minimae. The 

 aperture by which the blood leaves it is the tricuspid orifice. 



The orifice of the superior vena cava is in the upper and 

 posterior part of the atrium, at the level of the third right costal 



