THE VEINS. 



23 



^ Lift up the ventricle and turn it forwards so as to expose the 

 sinus venosus. 



iv. The sinus venosus is a thin-walled sac, lying dorsal 

 to the ventricle and behind the auricles ; it 

 receives the three large venae cavae. 



2. The pulsation of the heart. 



a. Note that the contractions of the heart continue some 



time after the frog has been killed, or even after the 

 heart is completely removed from the body. 



b. Note the character of the heart's pulsations : a regularly 



alternating series of contractions and dilatations. 

 C. Note further that in each contraction or systole of the 

 heart all four divisions of the heart contract, but not 

 simultaneously. The sinus venosus contracts first, 

 then the two auricles, then the ventricle, and finally 

 the truncus arteriosus. 



B. The Veins. 



. f[S 4- Diagrammatic figure of the venous system of the frog, from the 

 ngnt side. 



a, stomach: a.v, anterior alxlominal vein : h, bladder: ?xv, brachial 

 vein :c.l, cloaca! aperture : c.v, cardiac vein : d, large intestine • e, liver • 

 e.v, external jugular vein : f.v, femoral vein : g, gall bladder : h, spleen • 

 t.c, posterior vena cava : i.v, innominate vein : j.v, internal jugular vein • 

 Lp, Lett pelvic vein : m.r, musculo-cutaneous vein: o, kidney: ».r, hepatic 

 portal vein : r.p, right pelvic vein : r.v, right renal portal vein : -s, sinus 

 venosus : s.c, sciatic vein : s.v, subclavian vein : t, tongue : t.a, truncus 

 arteriosus : u, right auricle : v, ventricle : v.v, vesical veins. 



