70 A MANUAL OF ZOOLOGY 



of the eyes. Do they have eyelids? Is the iris colored? 

 Is there a nictitating membrane? Do you find indications 

 of ears on the outside of the head? Open the mouth and 

 notice the beak. Do you find any teeth? Find the opening 

 into the trachea and the posterior part of the floor of the 

 mouth. Behind thi? find the opening into the oesophagus. 

 Notice how the head and the neck can he withdrawn into 

 the shell and become encased in folds of skin surrouriSing 

 the neck. How does the length of the neck compare with 

 that of the animals already studied? Note the cavities 

 in the sides of the body into which the legs and the tail 

 may be drawn. Do you find scales on the legs, neck, or 

 tail? Find well developed claws on each digit. How many 

 are there on each foot? Are they web-footed? Cut through 

 the bridges with a bone forceps. Cut the plastron loose 

 from the skin and other attachments. After removing the 

 plastron notice the arrangement of the muscles attached 

 to its under side. Separate them carefully and observe 

 that they are arranged in pairs and determine the action 

 of each pair as nearly as possible. Dissect them away 

 so as not to disturb the underlying structures. Over the 

 ventral part of the body the peritoneum will be fqund. 

 Observe that the pectoral girdle seems to be separate 

 along the mid-ventral line. Dissect away the muscles 

 covering them. Then putting the thumbs under them 

 and twisting the fore legs at the same time, they may be 

 turned forward out of the way without injuring them. Back 

 of the posterior edge of the pectoral arch a little to the 

 right of the medial line find the heart, Inclosed in a tough 

 membrane, the pericardium. Open this and observe the 

 , large ventricular part of the heart, anterior to which is a 

 pair of distinctly separate auricles. From the antero-ven- 

 tral part of the ventricle observe the arteries passing be- 

 tween the auricles. Notice that what appears to be the 

 main trunk given off from the ventricle is in reality com- 

 posed of a number of distinct arteries bound together. By 

 careful dissection demonstrate this point. Is there any 

 indication- of a conus arteriosus? Dorsal to the aurfcles 

 is the sinus venosus. Remove the heart by severing the 

 arteries about one eighth of an inch from the heart, and 

 the veins immediately back of the sinus. 



