HEART 



413 



come into use, its position can still be recognised as a thin 

 area (fossa oralis) in the atrial septum, surrounded by a circular 



FIG. 317. HEART OF Ornithorhynchu* psiradoxu*. From the dorsal side. 



(After Rose.) 



Ao, aorta ; L.v, pulmonary veins; P.d, P., pulmonary arteries; R.V.h, right 

 atrium; Spi, Spatium intersepto-valvulare ; V.c.c, coronary vein; V.c.i, 

 postcaval ; V. c.. ..*, coronary sinus ; V.c.s.s, V.c.s.d, precaval veins. 



ridge (annidus oralis}. Extending from this to the base of the 

 postcaval and right precaval respectively are two more or less well- 



Y.C.S. 



FIG. 318. HEART 01 Hi .MAN FO-;TI:S (8TH MONTH). A, from the right, and B, 

 from the left side. (After Ruse.) The walls of the atrium and ventricle are 

 partly removed in each figure. 



A.o, aorta ; D.B, ductus Botalli (ductus arteriosus) ; F.o.v, foramen ovale ; L. V, 

 left atrium ; L.r, pulmonary vein : P, P.'/, P., pulmonary artery ; Va.s, 

 left sinu-auricular valve, fused with the septum atriorum (j"a, V.a.f) ; 

 Va.Th, Thebesian valve, in direct connection with the Eustachian valve 

 ( Va.E) ; V.c.c, coronary vein ; V.c.i, postcaval ; I'.c.x, left precaval. 



marked folds, known as the postcaval (Eustachian) valve and the 

 valve of the coronary sinus (Thebesian valve) respectively (Fig. 



