THE FROG 



55 



Now, just as has been explained in regard to the necessity of the 

 heart having an arterial supply of blood to its own walls in addition to 

 that which it pumps from its cavities, so the liver and kidneys must also 



r.au.-- 



tr.a. } - 



si. 



--i.v.c. 



Fig. 10. The Frog's Heart. 



A, seen from the ventral side ; B, from the dorsal side ; C, heart opened and viewed from ventral side. 

 (The ventral wall of the truncus, ventricle, and auricles has been removed). 



A. c.a, carotid arch ; car, carotid artery ; c.gl, carotid gland ; La, lingual artery ; 

 pc.a, pulmocutaneous arch ; pm, pericardium ; r.au, l.au, right and left auricles ; 

 s.v.c, superior vena cava ; y.a, systematic arch ; tr.a, truncus arteriosus ; v, ventricle. 

 B. i.v.c., inferior vena cava ; p.v., pulmonary veins ; r.au., l.au., right and left 

 auricles ; s.au., opening from sinus to right auricle ; s.v.c., superior vena cava ; s.v., 

 sinus venosus ; tr' ., branches of truncus cut across; v., ventricle. 



, C. au.v., Auriculo-ventricular valves ; c.a., carotid arch ; c.ao., cavum aorticum ; 

 ch.i., chordae tendine'se ; l.au., left auricle ; o.p.v., opening of pulmonary vein ; 'o.pc., 

 opening of dorsal division of synangium, by which blood passes from the cavum 

 pulmocutaneum to the pulmocutaneous arch ; pc.a., pulmocutaneous arch ; r.au., 

 right auricle ; s.au., sinu-auricular opening with valves; si., first row of semilunar 

 valves; si'., semilunar Valves of second row; si' .1, the semilunar valve from which 

 the spiral valve starts ; the line points to a small portion of the valve which has 

 been cut open; si' .2, small semilunar valve at end of cavum pulmocutaneum; si',3, 

 a small part of a large semilunar valve, of which the rest extends across that por- 

 tion of the front wall of the truncus which has been removed ; sp.v., spiral valve ; 

 sy.a., systemic arch; tr.a., wall of truncus arteriosus; tr' ., one of the two bundles 

 of arteries into which the truncus divides ; v., ventricle. (Redrawn from Borradaile. ) 



