EXTERNAL FORM OF THE HEART. 



303 



anterior surface is convex in its general form ; it is turned upwards as well 

 as forwards, and is directed towards the sternum and costal cartilages : 

 from these, however, it is partly separated by the lungs, the forepart of 

 these organs advancing over it to some extent, and encroaching still farther 

 during inspiration, so as in that condition to leave usually not more than 

 two inches square uncovered. The posterior, which is also the under surface, 

 is flattened, and rests on the diaphragm. Of the two borders or margins 

 formed by the meeting of the anterior and posterior surfaces, the right or 

 lower border, called maryo acutus, is comparatively thin, and is longer than 

 the upper or left border, which is more rounded and is named margo 

 obtusus. 



A deep transverse groove, the auriculo-ventricular furrow, interrupted in 

 front by the root of the pulmonary artery, divides the heart into the 

 auricular and the ventricular portions ; and on the ventricular portion two 

 longitudinal furrows indicate the position of the anterior and posterior 

 borders of the septum which divides one chamber from the other. 



Fig. 228. VIEW OF THE HEART 

 AND GREAT VESSELS FROM 

 BEHIND (fromR.Quain). ^ 



1, posterior surface of the 

 right ventricle ; 2, the same of 

 the left ; 3, placed on the back 

 of the right pulmonary artery 

 near the division of the primary 

 trunk ; 3', branches of the 

 right pulmonary artery passing 

 into the root of the right lung ; 

 3", the same of the left; 4', 

 back part of the arch of the 

 aorta ; 4", descending thoracic 

 aorta ; 5, part of the right 

 auricle ; 6, is placed on the 

 division between the right and 

 left auricles ; 7, superior vena 

 cava ; 7', left vena inuominata ; 

 8, trunk of the inferior vena 

 cava ; 9, right large hepatic 

 vein; 10, 11, 12, right pul- 

 monary veins ; 13, 14, lef c 

 pulmonary veins; +, +, pos- 

 terior branches of the right and 

 left coronary arteries. 



The auricular portion, situated above and behind the transverse furrow, is 

 thin and flaccid, and is immediately connected with the great veins ; it is 

 divided by an internal septum into two distinct cavities, which have received 

 the names of the right and left auricles, from the circumstance that each is 

 provided with an appendage somewhat resembling the ear of a dog. The 

 ventricular portion, placed below and in front of the transverse groove, is 

 somewhat conical, flattened on its posterior or under surface, has very thick 

 walls, and is connected with the great arterial trunks. The two longitudinal 

 furrows, which mark its division into a right and left chamber, situated one 

 on the anterior, the other on the posterior surface, extend from the base of 

 the ventricular portion, in a direct course, and are continuous one with the 

 other a little to the right of the apex, which is thus formed entirely by the 

 wall of the left ventricle. The anterior longitudinal furrow is nearer to 



