THE HEART 



The sinu-auricular aperture (Fig. 6, SV) 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 dis- 

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

 arteriosus, and of the auricles and ventricle have been removed. (From 

 a drawing 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, l6ft 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 tnmcus 

 arteriosus ; PV, opening of pulmonary vein into left auricle : RA, right 

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

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

 right auriple ; V, ventricle. 



C 



