COMPARATIVE ANATOMY 47 



Slit open the spiral valve and observe the large spiral fold which 

 serves to retard the passage of food, and thus secures more com- 

 plete digestion and absorption. 



5. Liver, large and oily, and consisting of several lobes united 

 at the anterior end. The gall bladder, usually recognizable by 

 its greenish color, lies embedded in the right side of the smallest 

 lobe of the liver. Trace the hile duct. It enters the intestine at 

 the point where the duodenum joins the spiral valve. 



6. Pancreas, a pale bilobed mass, one part of which lies on 

 the duodenum and the other, a more elongated portion, lies 

 between the stomach and spiral valve. The pancreatic duct may 

 be difficult to find. It is a short, white duct on the dorsal side 

 of the more compact lobe of the pancreas, sometimes embedded 

 in the tissue, and enters the anterior end of the spiral valve. 



7. Spleen, the dark colored, triangular organ attached to the 

 stomach. This structure is associated with the organs of 

 circulation. 



Before replacing the shark in its container remove the major 

 portion of the liver, leaving the base of the liver and the gall 

 bladder and bile duct intact. Removal of the liver will aid in 

 preventing the specimens from becoming oily. 



Digestive and Respiratory Organs of Necturus 



Open the body cavity by making a longitudinal incision from 

 one side of the anus through the pelvic girdle to the pectoral 

 girdle. Spread apart the two flaps; cut them off if necessary. 

 Identify the following organs: liver, gall bladder and bile duct, 

 stomach, pyloric valve, small intestine, large intestine, cloaca, 

 pancreas and spleen. Also, locate the lungs. These are a pair 

 of elongated, thin, semi-transparent structures lying dorsal to the 

 liver and stomach. 



Cut through the lower jaw and gill arches on each side and 

 expose the mouth cavity and pharynx. Find the posterior nares, 

 the internal openings of the nasal passages. These are located 

 at the posterior ends of the rows of teeth and are covered with 

 small flaps of skin that act as valves. The tongue is supported by 

 the hyoid arch. The walls of the pharynx are pierced by two 

 pairs of gill slits. The walls of the gill slits, unlike those of the 



