138 VERTEBRATE ZOOLOGY 



carry blood which is predominantly venous,— by the pulmonary 

 artery to the lungs, and by the left aorta largely to the stomach 

 and intestine. The right aorta, leaving the left side of the ven- 

 tricle, carries blood which is predominantly arterial to the remain- 

 ing tissues and organs of the body. 



Exercise 9. Draw a diagram showing the internal structure of the 

 heart so far as observed. 



The Digestive System. This system is composed of the following 

 organs : the mouth, pharynx, oesophagus, stomach, small intestine, 

 large intestine, and cloaca, and the liver and pancreas,— two large 

 glandular organs which communicate with the small intestine. 



With a scalpel cut through the pelvis in the median line. Inas- 

 much as the pelvic bones of the right and left sides are united in 

 the median line by a cartilaginous symphysis, this will be easily 

 done. Pull the two halves of the pelvis as far apart as possible 1 

 and separate the tissues beneath, thus exposing the cloaca. 



Observe the extent of the cloaca. It will be seen to be a mus- 

 cular tube passing beneath the pelvis. At its anterior end it is 

 continuous with the rectum, the posterior division of the large in- 

 testine. The large urinary bladder is joined with its ventral wall 

 by a narrow neck. The urinary and genital ducts join its dorsal 

 wall, and the penis, in the male, is a specialized portion of its 

 ventral wall. 



Turn the liver forward, and note the stomach beneath its left 

 border. The anterior end of the stomach, where the oesophagus 

 joins it, is the cardiac end ; its posterior end, where it opens into 

 the small intestine, is the pyloric end, and is marked by a constric- 

 tion. The anterior end of the small intestine, which lies between 

 the pylorus and the bile duct, is called the duodenum. Note the 

 gall bladder in the right lobe of the liver, and the main bile duct 

 which joins it with the duodenum. The green bile may often be 



a The pectoral and pelvic girdles may conveniently be kept out of the way 

 while the dissection of the viscera is progressing, as follows : Tie a stout string 

 around the right pelvic girdle ; pass it back over the carapace to the left pectoral 

 girdle, then over the carapace to the right pectoral girdle, and back again over 

 the carapace to the left pelvic girdle. Pull it as tight as possible around all 

 these girdles and fasten it to the last one. 



