THE HEART 619 
The coronary groove (Sulcus coronarius)! indicates the division between the atria 
and the ventricles. It almost completely encircles the heart, but is interrupted at 
the origin of the pulmonary artery. The longitudinal grooves,’ right and left, 
correspond to the septum between the ventricles. The left longitudinal groove 
(Sulcus longitudinalis sinister) is left-anterior in position. It begins at the coronary 
groove, behind the origin of the pulmonary artery, and descends almost parallel to 
the posterior border. The right longitudinal groove (Sulcus longitudinalis dexter) 
is right-posterior in position. It begins at the coronary groove, below the termina- 
Pulmonary artery 
Pulmonary veins —— 
left right 
branch branch 
Vena azygos 
Left 
ventricle 
Right lon- 
gitudinal 
groove 
Coronary groove 
Fic. 543.—Heart or Horse; Ricur View. HARDENED in situ. 
Line of reflection of serous pericardium dotted. Epicardium and subepicardial fat have not been removed from heart. 
Left ventricle is considerably contracted. 
tion of the posterior vena cava and passes toward the apex, but ends about an inch 
and a half (ca. 3-4 cm.) above the latter. Thus the two grooves do not meet. 
The grooves are occupied by the coronary vessels and a variable quantity of fat. 
The left groove is opposite to the fourth rib, and the right one is opposite to the fifth inter- 
costal space above and the sixth rib below. 
Size and Weight.—The average weight of the heart is about nine pounds 
(ca. 4 kg.) and is about 0.7 per cent. of the body-weight. There is, however, 
great range of variation in apparently normal specimens. 
1 Also termed the atrio-ventricular or auriculo-ventricular groove. 
? Also termed the interventricular grooves. 
