THE HEART. 



31 



The sinu-auricular aperture (Fig. 6, S.V.) leading from the 

 sinous venosus to the right auricle, is a transversely oval opening, 

 guarded by imperfect anterior and posterior valves, in the 

 ventral wall of the sinus venosus, close to its anterior end, and 

 very nearly in the median plane. 



CSP 



Fig. 6. The frog s heart seen from the ventral surface, and dissected 

 so as to show its structure. The ventral walls of the truncus arteriosus 

 and of the auricles and ventricle have heen removed. (From a drawin"- 

 by Dr. Hurst.) * 



A,_ auriculo-ventricular aperture and one of its valves : B, aperture 

 leading from ventricle to truncus arteriosus, with one of its valves : 

 C, left carotid arch : C, style passed down right carotid arch into the 

 truncus arteriosus : LA, left auricle : P, left pulmo-cutaneous arch • 

 P'P'. style, passed down right pulmo-cutaneous arch into the truncus 

 arteriosus : PV, opening of pulmonary vein into left auricle : RA, rio-ht 

 auricle : S, left systemic arch : S', style passed down right systemic 

 arch into the truncus arteriosus : SV, opening from sinus venosus into 

 right auricle : V, ventricle. 



