THE HEAET. 



871 



An oblique groove, the sulcus coronarius, runs transversely to the long axis 

 of the organ ; it separates the postero-superior or atrial portion from the antero- 

 inferior or ventricular part. The separation of the atrial portion into right and left 

 chambers is marked, externally, at the base of the heart only, where an indistinct 

 interatrial groove exists. The division of the ventricular part into right and left 

 ventricles is more definitely marked on the surface by anterior and an inferior 

 longitudinal sulcus which meet at the inferior border to the right of the apex. 



The heart lies in the middle mediastinum. It rests below on the diaphragm, 

 and is enclosed in the pericardium, which intervenes between it and the neighbour- 

 ing structures. Its long axis, from base to apex, runs obliquely from behind 

 forwards, downwards, and to the left. 



Basis Cordis. The base, which is formed by the atria, and almost entirely by 



Ligamentum arteriosum 



Aorta 



Left pulmonary artery 



Vestigial fold 

 (Marshall) 



Left pulmonary veins 



Right pulmonary artery 

 Superior vena cava 



Circumflex 



branch of left 



coronary artery 



Left marginal artery 



ight pulmonary veins 



Sulcus terminalis 



Right atrium 



Inferior vena cava 



Left ventricle ^ 



Right ventricle 



Coronary sinus 



7 50. THE BASE AND DIAPHRAGMATIC SURFACE OF THE HEART, showing the openings of the great 

 vessels and the line of reflection of the serous pericardium in a formalin hardened preparation. 



the left atrium, is directed upwards, posteriorly, and to the right. It lies anterior 

 o the descending thoracic aorta, the oesophagus, and the lower right pulmonary 

 vein, which separate it from the bodies of the sixth, seventh, and eighth thoracic 

 vertebrae. 



On the whole the base is somewhat flattened. It is irregularly quadrilateral 

 in outline, and the terminations of the superior and inferior venae cavse and the 

 four pulmonary veins pass through it. The opening of the superior vena cava is 

 situated at the upper right angle, that of the inferior cava occupies the lower 

 angle on the right side ; between and a little to the left of those openings are the 

 orifices of the two right pulmonary veins, and immediately to the right of the 

 latter is the indistinct posterior interatrial sulcus, which descends to the left 

 of the orifice of the inferior vena cava. The openings of the two left pulmonary 

 eins are situated near the left border of the base. The portion of the surface 

 which lies between the right and left pulmonary veins forms the anterior boundary 

 of a section of the pericardial cavity called the great oblique sinus. 



