64 A MANUAL OF ZOOLOGY 



a sketch of the alimentary canal with all of its accessory 

 organs. 



THE CIRCULATORY SYSTEM— Pith a frog. -Lay 

 him on his back and open the ventral wall to expose the 

 heart just under the sternum. Study the beat of the heart. 

 Do all parts of the -heart beat at the same time? De- 

 scribe the heart' beat. Note the four divisions of the 

 heart: the anterior part, the auricles; the ventricle; the 

 truncus arteriosus. How many auricles? What is the 

 relation of the ventricle to the auricles? The truncus ar- 

 teriosus arises from the right anterior border of the ven- 

 tricle. Trace this across the auricles. Dorsal to th« heart 

 find a thin walled sac.'the sinus venosus. How many 

 vessels open into it? These are called venae cavae. Note 

 the pericardium. What is its relation to the heart? To 

 what is it fastened? What does it contain? Dissect the 

 veins first on account of their being filled with blood j this' 

 gives them a dark color. Dissect from the ventral surface 

 being careful not to injure the veins. Clean and pin them 

 out carefully as you go along. 



Veins Opening Into the Sinus Venosus — Into the right 

 side opens the right anterior vena cava. ■ This carries the 

 blood from what region? It is formed by three veins: 

 the external jugular, the innominate, and the subclavian. 

 The first receives blood from the tongue through the 

 lingual vein and from the lower jaw through the mandi- 

 bular vein. The second gets blood from the interior of 

 the skull by the internal jugular and from the arm by the 

 subscapular vein. The third' gets blood from the fore leg 

 by the brachial vein, and from the skin and back by the 

 musculo-cutaneous vein. Compare the left anterior vena 

 cava with the right. 



The posterior vena cava may be traced from between the 

 kidneys forward and dorsally to the liver, and finally to 

 its opening into the posterior end of the sinus. It receives 

 blood from the hepatic veins. How many are there? Trace 

 the renal veins. Into w;hat do they empty? Trace also the 

 ovarian, and the spermatic veins. Locate the pulmonary 

 vein. Note that it is formed by two veins, one from each 

 lung, and that it empties directly into the left auricle. 



