622 BLOOD-VASCULAR SYSTEM OF THE HORSE 
on a curved crest, the crista terminalis, which indicates the junction of the primi- 
tive sinus reuniens of the embryo with the atrium proper, and corresponds with the 
suleus terminalis externally.!. The openings of the venee cave are valveless. A 
ridge, the intervenous crest (Crista intervenosa),? projects downward and forward 
from the dorsal wall just in front of the opening of the posterior vena cava; it 
tends to direct the flow of blood from the anterior vena cava to the atrio-ventricular 
Aorta 
Left pulmonary artery 
Right pulmonary artery 
: ‘es Pulmonary vein 
me — Posterior vena cava 
Fie. 546.—Lerr Sipe or Heart or Horse, OPENED uP BY REMOVAL OF Part oF WALL. 
{.s., Left atrium; Au. s., left auricle; V, V, V, bicuspid valve; V. s., left ventricle; M, M, moderator bands; P, } 
P, papillary muscles; 1, 2, great cardiac vein and circumflex branches of coronary arteries; 3, position of foramen ovale 
of fetus; 4, 4, openings of pulmonary veins (chiefly cut away); 6, atrio-ventricular orifice; 6, arrow points toward | 
aortic orifice. 
opening. The fossa ovalis is a diverticulum in the septal wall, at the point of | 
entrance of the posterior vena cava, bounded laterally by a concave margin (Limbus | 
fossxe ovalis). The fossa is the remnant of an opening in the septum, the foramen — 
ovale, through which the two atria communicate in the foetus. 
1 The crista terminalis is shown, but not marked, in Fig. 545; it is almost opposite (anterior) | 
to the intervenous crest. The suleus terminalis is commonly indistinct except near the vene 
CAV. 
* Also termed the tubercle of Lower. 
