THE HEART 



527 



right of the median plane and three-fifths to the left. The long axis (from the 

 middle of the base to the apex) is directed downward, backward, and somewhat to 

 the left. The base (Basis cordis) is directed dorsally and lies a little above the 

 middle of the dorso-ventral diameter of the thorax. It is opposite to the ribs from 

 the third to the sixth inclusive. The apex (Apex cordis) lies above the last segment 

 of the sternum, and is separated by a very short interval from the sternal part of 

 the diaphragm. The anterior border (Margo cranialis) is strongly convex and is 

 directed obliquely downward and backward; its lower part is parallel with the 

 sternum. The posterior border (Margo caudalis) is much shorter, nearly vertical, 



Pulmonary ( right branch 



Vena azygos 



Pvlmonary veins 



artery { left branch 





Left 

 ventricle 



Right lon- 

 gitudinal 

 groove 



""^ntr. 



Coronary 

 groove 



Fig. 420. — He.\rt of Horse, Right View. Hardened in situ. 



Line of reflection of serous pericardium dotted. Epicardium and subepicardial fat iiave not been removed from 



lieart. Left ventricle is considerably contracted. 



and is opposite to the sixth rib or intercostal space. The surfaces, right and left 

 (Facies dextra, sinistra), are convex and are marked by grooves which indicate 

 the division of the heart into four chambers, the two atria above and two ven- 

 tricles below. The left surface (covered by the pericardium) is in contact with 

 the lower third of the chest-wall from the third to the fifth intercostal space. On 

 the right side the cardiac notch of the lung is smaller and further forward, so that 

 the area of contact is at the third and fourth ribs. 



The coronary or atrio-ventricular groove (Sulcus coronarius) indicates the 

 division between the atria and the ventricles. It almost completely encircles the 



