THORACIC CAVITY 



atrium. The muscular ridges, 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 minimse. The 

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



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



Vena azygos 



Pericardium 



Superior vena cava 



' ' Right 

 bronchus 



Right 



pulmonary 



artery 



Musculi pectinati 

 Crista terminalis 



Diaphragm 



Sinus venarum 

 of right atrium 



Inferior vena 

 cava 



Hepatic vein 



FIG. 43. Sagittal section through the Right Atrium of the Heart and 

 the Root of the Right Lung. 



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

 cartilage. 1 It is entirely devoid of any valvular arrangement. 

 Immediately below it, on the posterior wall of the atrium, in 

 a well -fixed heart, will be found a rounded prominence, 



1 In the specimen shown in Fig. 46 it was at the level of the fourth 

 rostal cartilage. 



