4 VERTEBRATE ZOOLOGY 



in front of these pores is a conical median projection. This is the 

 urogenital papilla in the male and contains the outlet of the uro- 

 genital organs, and in the female the urinary papilla, which con- 

 tains only the outlet of the kidneys. The two genital openings in 

 the female are situated one on each side of the papilla. At the 

 front end of the cloaca is the opening of the rectum, the hinder end 

 of the digestive tract. The head of the animal extends back to the 

 first gill slit ; the anus forms the boundary between the trunk and 

 the tail. 

 Exercise 1. Draw a side view of the animal, and label the organs. 



Exercise 2. Draw a dorsal view of the head, showing the distribution 



of the mucous canals. 

 Exercise 3. Draw a ventral view of the head, showing the mucous 



canals and the other features. 



The Internal Organs. Determine the exact location of the pec- 

 toral and pelvic girdles, which support the fins of the same name. 

 Make an incision through the body wall in the midventral line 

 from the pectoral girdle to the pelvic girdle; then continue the 

 incision straight through the pelvic girdle to a point immediately 

 in front of the anus, taking care not to cut too deeply. Just back 

 of the pectoral girdle make a transverse incision in each side of 

 the body wall ; make similar incisions in front of the pelvic girdle. 

 Place the animal on its back, with its head away from you, on a 

 dissecting board or in a large dissecting pan. Pin down the two 

 flaps of the body wall firmly to the right and left, and thus expose 

 the organs which lie in the abdominal cavity. 



Study the position of these organs, but without disturbing them. 

 The entire body cavity is divided by a vertical partition into two 

 chambers : the small pericardial chamber, at the anterior end be- 

 tween the gills, in which lies the heart ; and the large abdominal 

 chamber, which contains the greater part of the viscera ; the peri- 

 cardial chamber has not yet been opened. These cavities are lined 

 by a serous membrane which is called the pericardium in the peri- 

 cardial chamber and the peritoneum in the abdominal chamber. 

 The partition separating these chambers is situated just beneath 

 the pectoral girdle and is called the false diaphragm. 



