90 THORAX 



formed by the anterior and lateral walls of the right atrium 

 is turned forwards a vertical ridge will be noted on its 

 inner surface. It is the crista terminalis, which corre- 

 sponds in position with the sulcus terminalis on the outer 

 surface. It marks the boundary between the anterior part 

 of the atrium, the atrium proper, and the posterior part, which 



Aorta . - 

 Superior vena cava - pi 



Upper rig! 

 pulmonary vei 



Lower right 



pulmonary 



vein 



Limbus fossse ovali 



Fossa oval is 



\ Tricuspid orifice 



Opening of coronary sinus 

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



FIG. 42. The Right Atrium. Part of the posterior wall and the whole 

 of the right lateral and anterior walls have been turned forwards. 



is known as the sinus venarum because the great veins of 

 the body and heart open into it (Figs. 42, 43). The 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 sinus venarum is smooth, the 

 rest of the wall of the atrium is rendered rugose by a large 

 number of muscular ridges which commence at the crista 

 terminalis and run forwards to the right margin of the 



