16 THE SKATE 



At the anterior end of the cavity is the liver, which is 

 composed usually of three lobes of about the same size. 

 In the angle between the median and the right lobes of 

 the liver is the gall bladder. Dorsal to the liver and on the 

 skate's left side is the j -shaped stomach. It is continuous 

 with the esophagus and is partly concealed by the lobes of 

 the liver. The anterior part of the stomach is the cardiac 

 portion while the smaller bent portion is the pyloric region. 

 The latter terminates the stomach in a sharp constriction, 

 the pylorus. The remainder of the digestive tract to the 

 anus is the intestine. The first section of the intestine just 

 beyond the pylorus is the duodenum. Beyond the duode- 

 num the intestine becomes enlarged and the lines of inser- 

 tion of the spiral valve, which is within the intestine, are 

 visible. 



Near the posterior end of the intestine is the small 

 cylindrical rectal gland which is attached to the intestine 

 by a short duct. The intestine is divisible into two parts, 

 the anterior intestine (small intestine) and the posterior 

 intestine (large intestine). The place of separation is at 

 the rectal gland. The terms small and large intestine may 

 be given to these parts out of consideration for their 

 homology, but in the skate they are just the reverse in 

 actual size. The posterior intestine is very short and opens 

 by the anus into the terminal chamber, the cloaca, which in 

 turn opens to the exterior by means of the cloacal aperture. 



B. The Derivatives of the Digestive Tract. 



Along the digestive tract are numerous organs and glands 

 which have been derived from the tract. Some of these 

 will be considered here. A series of derivatives have al- 

 ready been encountered, including the visceral pouches and 

 the gills. 



The thyroid gland is an outgrowth from the ventral wall 



