622 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



on a curved crest, the crista tenninalis, which indicates the junction of the primi- 

 tive sinus reuniens of the embryo with the atrium proper, and corresponds with the 

 sulcus terminalis externally.' The openings of the vense cavse 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 



Pulmonary vein 



Posterior vena cam. 



Fig. 546. — Left Side of Heart of Horse, Opened ttp by Removal of Part of Wall. 

 A.S., Left atrium; Au. s., left auricle; T', V, V, bicuspid valve; V. s., left ventricle; JVf, M, moderator bands; P, 

 P, papillary muscles; 1, 2, great cardiac vein and circumflex branches of coronary arteries ; 3, position of foramen oval& 

 of foetus; .4, .J, 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 

 fossae 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 ahnost opposite (anterior) 

 to the intervenous crest. The sulcus terminalis is commonly iadistinct except near the ven£& 

 cavEe. 



^ Also termed the tubercle of Lower. 



