138 PRACTICAL ZOOLOGY. 



and from front to back. Hold the heart between the 

 two hands, with its apex up, and again compare the 

 firmness of the two ventricles. 



11. Turn the heart to the left and examine the right auri- 

 cle ; find a large, red-walled tube entering it from the 

 front; this is the superior vena cava, which brings 

 the blood from the head, neck, and fore limbs to the 

 right auricle. Trace this vein forward to the point 

 where it was severed (or if this is not readily found, 

 prick a hole in it) ; insert the point of the blowpipe, 

 pinching the vein closely about it, and inflate the 

 vein. Meanwhile watch closely the posterior part of 

 the auricle ; there should be discovered another tube 

 entering the auricle from behind, the vena cava infe- 

 rior, which passes forward through the diaphragm ; 

 find where it was severed, and inflate the right auricle 

 through it, holding the vena cava superior if neces- 

 sary. By this inflation the outlines of the right auri- 

 cle and ventricle should be determined. 



12. Turn the heart to the right and observe a large, light- 

 colored tube arising from the base of the right ventri- 

 cle between the two auricles; this is the pulmonary 

 artery ; again turn the heart to the left and raise the 

 right auricle ; find a second large artery arising from 

 the center of the base of the heart ; this is the main 

 artery, or aorta. Carefully separate the aorta and 

 pulmonary artery above the base of the heart. 



13. Trace the aorta as it arches over and runs down 

 between the two lungs behind, alongside the gullet ; 

 find where it was cut off. With knife and scissors 

 cautiously clear away the whole arch of the aorta 

 from the surrounding tissues. 



14. From the arch of the aorta arise the branch or 



