XV 



THE CIRCULATORY SYSTEM 



265 



walled sinus venosus ; at the two anterior angles of the sinus 

 the precaval veins, or anterior vena cava, enter; the poste- 



eangl m ^ 



au,.v.V 



FIG 72 -The heart of a frog cut open and seen from the ventral side. 

 a a' bristle passed into the left carotid trunk; au.v.v, aunculo-ven- 

 tricular valves; b,b', bristle passed into the left systemic trunk ; c,c 

 bristle in left pulmo-cutaneous trunk; car. a, carotid artery; car.gl, 

 carotid gland; cart, bulbus cordis (conus arteriosus of some authors) ; 

 carJr, carotid trunk; Lau, left auricle; /^.a, lingual artery; /.*, longi- 

 tudinal or spiral valve ; pul.cu.tr, pulmo-cutaneous trunk; pui.v, open- 

 ing of pulmonarv veins; r.au, right auricle; s.au.ap, smu-auncular 

 aperture; sptaur, inter-auricular septum; z;, z/', valves; *, ventricle. 

 (From Parker and Haswell's Zoology.) 



rior apex receives the large postcaval vein, or posterior vena 

 cava. In front of the anterior margin of the sinus is the 

 pulmonary vein, which empties into the left auricle. 



