526 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



ribs. The anterior border of the base is opposite to the second intercostal space, 

 and the posterior border is opposite to the sixth rib or space. The base is related 

 to the great vessels, the trachea and its bifurcation, the bronchial lymph glands, 

 the oesophagus, and the vagus, left recurrent, and cardiac nerves. 



The two part.s of the .serous pericardium are, of course, continuous with each other at the 

 line of reflection on to the great vessels. The latter are covered in varying degree by the visceral 

 layer. The aorta and pulmonary artery are inclosed in a complete common sheath as far as the 

 bifurcation of the latter. A pouch passes inward between the pulmonary artery and the left 

 auricle, and is connected with another pouch which passes backward between the right auricle 

 and the aorta, thus forming the great transver.se sinu.s of the pericardium. The posterior vena 

 cava is covered on the right and })elow for a distance of an inch or a little more (ca. 3 cm.). The 

 pulmonary veins receive practically no serous covering. The epicardium is closely adherent to 

 the muscular tissue of the heart, but is attached to the vessels by loose tissue and fat, and hence 

 is easily dissected off them. 



THE HEART 



The heart (Cor) occupies the greater part of the middle mediastinal space. 

 Its shape is that of an irregular and somewhat flattened cone. It is attached at 



Brachiocephalic trunk 



/^^^>v Lig. aria 



Coronary 

 groove 





Pulmonary reins 





Artery 



Left 

 auricle 

 (appen- 

 dix) 



Coronary 



groove 



V'nus ar^^ 



4v Ii'i9ht " 

 Ventricle 



rio 



;l>S 



\S 



)ii 



I'dstcrior 

 bonier 



\ 



left > V 

 Ventricle ^ 



Left longitiulinal groove 



Fig. 419. — Hkart ok Horsk, Left View. Hardened in situ. 

 The dotted line indicates the line of reflection of the serou.s pericardium. The epicardium and subepicardial fat 



have not been removed from tlic heart. 



its base by the great vessels, but is otherwise entirely free in the pericardium. It 

 presents two surfaces, two border.s, a base, and an apex for description. 



In position the heart is decidedly asymmetrical, about two-fifths being to the 



