18 THE SKATE 



of incomplete overlapping cones. This formation greatly 

 increases the digestive and absorptive surface of the intes- 

 tine and makes a long intestine unnecessary. 



D. The Spleen. 



The spleen is a dark-colored organ located on the dorsal 

 side of the stomach at its bend. It is not a part of the 

 digestive system, but belongs to the category of lymph 

 glands of the lymphatic system. Its function appears to be 

 the destruction of foreign particles, bacteria and the like, 

 and the addition of white blood corpuscles to the blood 

 circulation. 



Drawing 10. Make an outline drawing of the digestive tract, 

 its derivatives and the spleen. 



E. The Mesenteries. 



The viscera are suspended and held in place by mem- 

 branes, the mesenteries or ligaments which are the exten- 

 sions of the pleuroperitoneum. The dorsal mesentery is 

 incomplete in the skate. It extends from the dorsal wall 

 to the anterior part of the stomach and the posterior part 

 of the esophagus as the mesogaster. It incloses the spleen 

 in an extension from the stomach, the gastrosplenic. 



A remnant, the lesser omentum, is all that is left of the 

 ventral mesentery, which typically is an outfolding from 

 the median ventral wall. It extends from the right side 

 of the stomach to the liver and is roughly divisible into two 

 parts: the hepatoduodenal, which extends from the duo- 

 denum and which contains the bile duct and blood vessels, 

 and the gastrohepatic, which extends from the stomach to 

 the liver. The falciform ligament is another remnant of 

 the ventral mesentery and is located at the anterior end of 

 the liver, extending from the midventral surface of the 

 liver to the midventral line of the body wall. 



