82 THORAX 



the posterior wall of the sinus. The anterior wall of the 

 oblique sinus is the posterior wall of the left atrium (Fig. 37). 

 If the dissector passes his left index finger into the transverse 

 sinus and the middle and index fingers of his right hand into 

 the oblique sinus, he will be able to convince himself that 

 the left atrium is the only structure which intervenes between 

 the cavities of the two sinuses. When he has satisfied 

 himself regarding this point, he should note that the lower 

 and posterior part of the coronary sulcus of the heart extends 

 across the lower part of the base between the posterior end 

 of the left ventricle and the lower end of the left atrium, 

 and that it is occupied by the coronary blood sinus, which 

 opens into the right atrium immediately to the left of the 

 upper end of the inferior vena cava. 



A complete examination of the base of the heart cannot 

 be made until the heart is removed from the thorax at a later 

 stage of the dissection, and the dissectors should pass now 

 to a consideration of the relation of the serous layer of the 

 pericardium to the great vessels which are entering or leaving 

 the heart (see Fig. 32). They have previously noted (p. 73) 

 that the visceral layer of the serous portion of the pericardium 

 covers almost every portion of the heart, the only part left 

 uncovered being the upper border of the left atrium, which 

 is in contact with the lower border of the right pulmonary 

 artery. 



To demonstrate again the lines of reflection of the 

 visceral into the parietal part of the serous pericardium, 

 seize the apex of the heart with the left hand and lift it 

 upwards. Then pass the fingers of the right hand along the 

 visceral layer on the inferior surface of the heart and upwards 

 along the posterior surface of the left atrium to the upper 

 margin of the oblique sinus, where, immediately below the 

 right pulmonary artery, the visceral layer passes backwards 

 and joins the parietal layer on the inner surface of the 

 posterior wall of the pericardium. Follow the parietal layer 

 on the posterior wall of the pericardium downwards with the 

 fingers. At the inferior end of the posterior wall they will 

 be carried forwards on the inner surface of the inferior wall, 

 or base, of the pericardium to the anterior wall, which should 

 be temporarily replaced in position. Then they must pass 

 upwards along the anterior wall, to the level of the upper 

 parts of the ascending aorta and the pulmonary artery, where 



