664 



PHYLUM CHORDATA : CLASS AMPHIBIA 



this. The complex mechanism is interesting because it 

 determines the course of the blood leaving the heart. 



As the heart continues to live after the frog is really dead, its con- 

 tractions can be readily observed. The sinus vcnosus contracts first. 



Fig. 382. — Venous system of frog. 



vt., I., Mandibular and lingual ; e.j., external jugular ; i.j., internal 

 jugular; scp., subscapular; in., innominate; scl., subclavian; 

 br., brachial ; m.c, musculo-cutaneous ; h.v., hepatic vein ; 

 h.p., hepatic portal ; a.a., anterior abdominal ; r.p., renal-portal ; 

 p.v., pelvic ; sc, sciatic ; /., femoral ; i.v.c, inferior vena cava ; 

 c, cardiac vein. 



• 

 then the two auricles simultaneously, and finally the ventricle and conus. 

 Although the ventricle receives both impure and pure blood, the 

 structural arrangements are such that most of the impure blood is 

 driven to the lungs, the purest blood to the head, and somewhat mixed 

 blood to the bodv. 



