618 



BLOOD-VASCULAR SYSTEM OF THE HOESE 



dorsal and middle thirds of the dorso-ventral diameter of the thorax. It is opposite 

 to the lateral wall of the thorax, from the second intercostal space or third rib to the 

 sixth rib or intercostal space. ^ The apex (Apex cordis) lies centrally above the last 

 segment of the sternum; it is half an inch or less (ca. 1 cm.) above the sternum and 

 about an inch (ca. 2-3 cm.) from the sternal part of the diaphragm. The anterior 

 border (Margo cranialis) is strongly convex and curves ventrally and backward; 

 the greater part is parallel with the sternum. The posterior border (Margo cau- 

 dalis) is much shorter, is nearly vertical, and is opposite to the sixth rib and inter- 

 costal space. The surfaces, right and left (Facies dextra, sinistra), are convex and 



lAg. arteriosum Pulmonary veins 



Brachiocephalic trunk / 



Left auricle 



Coronary 

 groove 



Posterior 

 border 



Coronary 

 groom 



Left longitudinal groove 

 Fig. 542. — Heart of Horse; Left View. Hardened in situ. 

 The dotted line indicates tlie line of reflection of the serous pericardium. The epicardium and subepicardial fat have 



not been removed. 



are marked by grooves which indicate the division of the heart into four chambers, 

 the two atria above and two ventricles below. The left surface (covered by the 

 pericardium) is related to the lower third of the chest-wall from the third to the 

 sixth rib. On the right side the cardiac notch of the lung is smaller, so that the 

 area of relation to the chest-wall extends from the third to the fourth intercostal 

 space. - 



^ The size and form of the heart vary according to the degree of its contraction and relaxa- 

 tion (systole and diastole). In subjects which have been bled and preserved by intravascular 

 injection of formalin solution the right side is usually fixed in diastole while the left is more or less 

 strongly contracted. The base may extend back to the seventh rib. 



^ The arrangement in this regard has been stated at greater length in the descriptions of the 

 lungs and the pericardium. 



