HEART 



413 



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

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



l-'n:. 317. HEART OF Omithorhynchus paradoxus. From the dorsal side. 



(After Ruse. ) 



Ao, aorta; L.i; pulmonary veins: P.d, /'..*, pulmonary arteries; E.V.h, right 

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

 postcaval ; F.c.s.s, coronary sinus ; IV.. >-..-, V.c.s.d, precaval veins. 



ridge (annulus ovalis}. Extending from this to the base of the 

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



B 



Vc.s. 



Va.s 



Va.Th.1 



Fi<;. 318. HEART or HUMAN F<KTUS (STH MONTH). A, from the right, and B, 

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

 partly removed in each tigure. 



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

 left atrium ; L.r, pulmonary s*ein ; P, P.d, P.*, pulmonary artery ; Vti.fi, 

 left sinu-auricular valve, fused with the septum at riorum (Sa, V.a.f) ; 

 I'ti.Th, Thebesian valve, in direct connection with the Eustachian valve 

 ( Va.E) ; V.c.c, coronaiy vein ; V.c.i, postcaval ; T'.c.*, left precaval. 



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

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



