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 paraliel 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 
Right atrium 
Left ventricle 
Right ventricle 
Fic. 606.—Heart or Pic, DiapHRAGMATIC SURFACE. 
1-6, Pulmonary veins; 6, left pulmonary artery; 7, 8, branches of right pulmonary artery; 9, vena azygos; 10, 
fat in coronary groove; 11, vessels and fat in right longitudinal groove; 12, 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 
UIncisura 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 intervenous 
crest is broad and rounded, not prominent, as in the horse. The musculi pectinati radiate from 
a distinct crista terminalis and form a highly developed network in the auricle. The fossa 
ovalis is extensive. There is a large moderator band in the right ventricle. 
