THE HEART 



735 



The heart is small in proportion to the body-weight, especially in fat animals. 

 Its weight in a large adult is usually less than a pound. It is broad, short, and blunt. 

 When hardened in situ it is compressed dorso-ventrally. The ventral or sterno- 

 costal surface (Facies sternocostalis) is only moderately convex; it overlies the 

 sternum from the second sternebra to the anterior part of the last one. The left 

 longitudinal groove is on its left part, and is almost parallel with the left border. 

 The dorsal or diaphragmatic surface is more convex. The right longitudinal groove 

 runs obliquely across this surface; it begins below the end of the posterior vena 

 cava and extends to the left border. There is often an intermediate groove on the 

 left border; it may extend to the apex, but it is frequently small and is sometimes 



Vena hemiazygos 

 Pulmonary artery 

 Left auricle 



Left venlrich 



Right atrium 



^ Eight ventricle 



Fig. 606. — Heabt of Pig, Diaphhagmatic Sukface. 



-S, Pulmonary veins; 6, left pulmonary artery; 7, 8, branches of right pulmonary artery; S, vena azygos; 10, 



fat in coronary groove; 2i, vessels and fat in right longitudinal groove; IS, apex. 



absent. The apex is blunt and is almost median; it overlies the anterior part of 

 the last sternebra, and is about a quarter of an inch (ca. 5-6 mm.) from the sternal 

 part of the diaphragm. When the ventricles are dilated, there is a notch at the apex 

 (Incisura apicis cordis). The lower border of the left auricle is marked by several 

 notches and is situated at a lower level than the right one. 



In the right atrium the large orifice of the vena hemiazygos is seen below that of the posterior 

 vena cava; the two are separated by a valvular fold with a concave free edge The mtervenous 

 crest is broad and rounded, not prominent, as in the horse. The muscuh pectmati radiate from 

 a distinct crista terminalis and form a highly developed network m the auricle. The fossa 

 ovaUs is extensive. There is a large moderator band m the right ventricle. 



