158 THE SPINY DOGFISH— THE SKATE 



A. The Alimentary System and Vascular System (pari). 

 Make a drawing showing the following parts : — 



(a) The liver, divided into two large lobes and a small intermediate lobe. 



It extends along the whole length of the abdomen. The gall-bladder 

 is situated in the intermediate lobe, and from it the bile-duct passes 

 backwards to open into the intestine some distance behind the 

 pylorus. [In Scyllium the liver is bilobed, and the gall-bladder is 

 lodged in the upper part of the left lobe. In the Skate the liver 

 is trilobed, and the gall-bladder is situated between the right and 

 median lobes.] 



(b) The stomach, a large J -shaped sac divided into a cardiac and a pyloric 



portion. 



(c) The small intestine (duodenum), a short and narrow region following 



the pyloric part and receiving the bile-duct and the pancreatic 

 duct. 



(d) The large intestine, following the small intestine. It is a wide tube with 



an internal fold, the spiral valve. 



(e) The rectum, the short terminal part of the large intestine, ending in the 



anus within the cloaca. Note the rectal gland attached to the dorsal 

 surface of the rectum. 



(/) The pancreas, lying in the bend between the short distal limb of the 

 stomach and the small intestine. It is long and narrow posteriorly, 

 but anteriorly it is rounded, and from this lobe the pancreatic duct 

 issues and at once enters the wall of the small intestine (at about 

 an inch distance from the pylorus). [In the Skate the pancreatic du£t 

 enters the intestine opposite the bile-duct.] Sometimes (in Acanthias) 

 the pancreas is not visible, being only slightly developed in the 

 intestine wall. 



{g) The spleen, a dark red body, attached by mesentery to the bend of the 

 stomach. 



{h) The cceliac artery, running backwards in the same mesentery as the bile- 

 duct, supplying the stomach and liver and pancreas. 



{i) The anterior mesenteric artery to the middle of the large intestine. [In 

 the Skate the superior mesenteric artery supplies the intestine, pancreas, 

 and spleen.] 



(j) The lieno-gastric artery to the loop of the stomach and the spleen. 



(/«) The hepatic portal vein (from intestine and spleen), passing alongside 

 the bile-duct and entering the liver about the median plane. 



(l) The gonad and genital ducts. Notice the slit like common opening of 

 the two oviducts (vestigial in the male) on the falciform ligament of 

 the liver. 



Note the peritoneum, and the way in v/hich the spleen is attached to the 

 stomach. The alimentary canal is attached to the dorsal wall of the 

 abdominal cavity by mesentery — i.e., a double sheet of reflected peritoneum ; 



