THORACIC CAVITY 



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separable into two parts a larger main portion, the atrium 

 proper or body ; and a long narrow prolongation, the auricle 

 (O.T. auricular appendage), which runs from the left margin 

 of the body forwards and to the right. The four pulmonary 



FIG. 58. The relations of the Heart and of its Orifices to the Anterior 

 Thoracic Wall. 



I to VII. Costal cartilages. 



A. Aortic orifice. 

 Ao. Arch of Aorta. 



C. Clavicle. 

 LA. Left atrium. 

 LV. Left ventricle. 



M. Mitral orifice. 



P. Pulmonary orifice. 

 RA. Right atrium. 

 RV. Right ventricle. 

 SVC. Superior vena cava. 



T. Tricuspid orifice. 



veins, two on each side, open into the left atrium. They enter 

 close to the upper ends of the lateral borders of the posterior 

 surface, and not uncommonly the right or the left pair may 

 fuse into a common trunk at the point of entrance. 



It has been noted previously that the left atrium forms 

 the greater part of the base of the heart, a small part of the 

 anterior or sterno-costal surface, and a still smaller part of 



