RAIA. 315 



spiracle and out over the gills. Breathing is therefore 

 independent of the mouth. 



If the skate be laid on its dorsal surface, and the skin 

 and underlying muscle be removed in the area lying between 

 the coracoid and pubic bars, the spacious abdominal cavity 

 will be exposed. In it lie freely the other portions of the 

 alimentary system. The (Esophagus entering the abdomen 

 at the front end leads into the large stomachy which is U- 

 shaped and inclined to the left. It is mainly hidden by the 

 spreading trilobed gland, the liver, which is attached at the 

 anterior part of the abdomen, but each lobe hangs free 

 posteriorly. From the opposite end of the stomach to the 

 oesophageal opening there arises the intestine, a tube of 

 varying calibre passing down to the cloacal aperture. Its 

 first portion, the duodenum, is short and leads into the very 

 wide ileum containing in its interior a spiral valve. The 

 last portion is the rectum, narrower than the intestine proper 

 and with no spiral valve. It opens into the cloaca. 



This alimentary canal has three important glands which 

 open into it. The liver has already been referred to. 

 Between its median and right lobes is a gall-bladder, from 

 which there passes a long bile-duct to open into the duo- 

 denum. The bile, secreted by the liver, is stored in the 

 gall-bladder and periodically discharged into the duodenum 

 by the bile-duct. Near the duodenum is a bilobed whitish 

 organ of moderate size, called the pancreas. It secretes 

 a digestive fluid which is discharged by a short pancreatic 

 duct into the commencement of the ileum on its dorsal 

 side. Lastly, near the termination of the rectum is a small 

 oval rectal gland opening into the rectum ; it may be excretory. 



Before leaving the alimentary system, the spleen, a dark- 

 red ductless gland near the stomach, should be observed. 

 Note also i\\Q portal vein, a large vein drairiing the stomach, 

 intestine, spleen and pancreas, and passing forwards to the 

 liver ; and the cceliac artery which supplies the stomach, 

 duodenum and liver with arterial blood. 



If the skin and muscles be removed from the area 



between the mouth and the coracoid bar, the pericardial 



Vascular ^^"^^^y ^"^^ be exposed. It communicates with 



the abdominal cavity by a pair of small canals, 



and the two cavities compose the perivisceral coelom. They 



