92 ELEMENTS OF COMPARATIVE ZOOLOGY. 



and pulmonary veins belong to the pulmonary circulation. 

 Add them to the sketch. 



Cut through the cavas, pulmonary vessels, and aorta, and 

 remove the heart. On the base on either side will be found 

 small lobes the auricles. Split the heart with a sharp 

 scalpel parallel to the horizontal plane of the animal, keep- 

 ing in mind which side of the organ was originally right, 

 and which left. Make out two pairs of cavities (usually 

 containing clotted blood, which should be carefully re- 

 moved). Which of these has the thicker walls the right or 

 the left ? The basal cavities are the auricles, the apical the 

 ventricles. Which parts, auricles or ventricles, would you 

 suppose to play the greater part in forcing the blood 

 through the circulation ? Study the connections between 

 auricles and ventricles. Do the two auricles connect with 

 each other ? Is the same true of the ventricles ? Notice 

 what vessels enter the left auricle. Where do the pre- 

 and postcava enter ? Where does the blood go from the 

 left ventricle ? Insert a diagram of the heart, with its 

 chambers, in the sketch of the circulation.* 



Between the common carotids is the ringed trachea, or 

 windpipe. Dissect it loose and cut near the head. Insert 

 a blowpipe in the hinder portion and inflate the lungs by 

 blowing. Are the rings of the trachea complete ? Trace 

 the trachea forward and notice enlarged anterior portion 

 (larynx), and just in front, and ventral to it, the hyoid 

 bone. Beneath the trachea (dorsal to it) is the oesophagus. 



Remove the skin from the head. Notice the large 

 muscles attached to the jaw, and just in front of the ear 

 the salivary (parotid) gland. Cut through the jaw muscles, 



* The heart of a cat, sheep, or pig will show these points much 

 better. 



