THE VEINS 



25 



lAft up the ventricle and twi'n its apex 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 vense 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. 



Bt, sy. 



Fig. 4.— Diagrammatic figure of the venous system of the frog, 

 from the right side. . , ■. L ^ 



a, stomach ; a.v, mt gior abdom inal vein ; b, bladder ; ^.ij. brachiaL 

 vein ; c.l, cloacal aperture j'^.w, cardiac vein; d, large intestine ; 

 e, liver ; e.v, external ]np"lgr y^in ; f,v, femoral vein ; g, gall-bladder ; 

 h, spleen ; i.C, P0Ste'- i"T "R^p, '■'""' : i.v, iTinnininate Y(;in ; j.v, jntRrnal 

 jiipnl pr vpin ; l.f, leftgelvis_jein ; m.v, TnTiiciiln-cutanenns vein ; 

 0, kidney -"^.w, hepatic portal vem ; r.p, right pelv''^ vein ; r.v. right 

 renal pqrta L-itein' : j . suihs venosus : s.c, sciyic vein ; s.v, ffihrlflvi^n 

 vein : t, tongue; t.a, truncus arteriosus ; », right auricle ; v, ven- 

 tricle ; v.v, vesical veins. 



