THE HEART. 



691 



great vessels communicates with its ventricle are guarded by special valves known as 

 the semilunar valves. 



The auricular portion of the heart rests upon the posterior part of the base of the 

 ventricular portion, and is best viewed from the posterior surface (Fig. 655J, since 

 it is almost completely hidden anteriorly by the two aortae. Like the ventricular 

 portion, it is composed of two separate chambers, which are not, however, very 

 apparent on surface view. These chambers are xho.' right and left auricles^ and com- 

 municate with the corresponding ventricles by auriculo-ventricular orifices guarded 

 by special auricido-ventricular valves. From the lateral part of the anterior sur- 

 face of each auricle a process, the auficiilar appendix., arises. These appendices are 



Fig. 655. 



Left common carotid artery 

 Left subclavian artery 



Innominate artery 



Left pulmonary 

 artery 



Vestigial fold 



Sup. left pulm. vein 

 Left auricular 



appendix 



Inf. left pulm. vein 



Coronary sinus 



Left ventric 



Azygos vein 

 Superior vena cava 



Right pulmonary 

 artery 



Superior 



Inferior 



right 



pulmonary 



vehis 



Left auricle 

 Right auricle 



Inferior vena cava 



Right ventricle 



Apex 

 Posterior aspect of heart hardened in situ ; showing lines of reflection of pericardium. 



slightly flattened prolongations of the auricles, and bend forward around the bases of 

 the aortae, which they slightly overlap in front ; they are the only portions of the 

 auricles visible upon the anterior surface of the heart. • Upon its superior surface the 

 right auricle receives the termination of a large venous trunk, the vena cava 

 superior, which returns to the heart blood from the head, neck, upper extremities, 

 and walls of the thorax ; while upon its posterior surface is the opening of another 

 large vessel, the vena cava inferior, which returns blood from the abdominal and 

 pelvic walls and viscera and from the lower limbs. The left auricle receives upon 

 its surface the four pulmonary veins arranged in pairs, one pair situated towards the 

 left portion of the auricle and the other towards the right. 



