164 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



part of the coelom. It is lined by a smooth shining membrane, the parietal peri- 

 toneum, which adheres closely to the inside of the body wall. The body wall 

 is seen to be composed of three layers: skin, muscles, and parietal peritoneum. 

 2. The viscera of the pleuroperitoneal cavity. Within 1 the cavity are a 

 number of organs or viscera, most of which belong to the digestive tract. At 

 the anterior end of the cavity is the large brownish or grayish liver. This con- 

 sists in the spiny dogfish of long left and right lobes and a small median lobe in 

 which is located the long greenish gall bladder. In the smooth dogfish, the liver 

 is subdivided into right and left lobes, the median lobe being absent; the gall 

 bladder is imbedded in the anterior part of the left lobe and is visible as a thin 

 place in the liver. In the skate the liver is composed of right, median, and left 

 lobes of equal length and size, and the gall bladder is situated in the angles between 

 the right and median lobes. Dorsal to the liver on the left side is the large 

 J -shaped stomach, often distended with food. (In some specimens the stomach 

 is everted into the mouth cavity and should be pulled back into the pleuroperito- 

 neal cavity by exerting a gentle traction on it.) The greater part of the stomach 

 consists of a large straight tube extending from the anterior end of the pleuro- 

 peritoneal cavity to a point somewhat posterior to the ends of the liver lobes. 

 It then makes a sharp bend, decreasing in diameter considerably, and extends 

 anteriorly, terminating in a constriction, the pylorus. Along the posterior margin 

 of the bend of the stomach (or in the skate on the dorsal side of the bend) is a 

 dark-colored organ, the spleen, a part of the lymphatic system. From the 

 pylorus the short intestine extends to the anus. The first part of the intestine 

 beyond the pylorus is called the duodenum. It extends for a short distance to 

 the right and then curves posteriorly. The bile duct, a long stout duct, is 

 easily seen descending from the gall bladder to enter the duodenum shortly 

 caudad of the bend. The bile duct accompanied by some blood vessels runs 

 in a strip of mesentery. It passes to the dorsal side of the duodenal wall and 

 runs for a short distance caudad imbedded in the wall before it penetrates into 

 the cavity of the duodenum. In the curve of the duodenum reposes the ventral 

 lobe of a white gland, the pancreas. The dorsal lobe of the pancreas, which is 

 long and slender in the spiny dogfish, reaching to the spleen, should be located by 

 raising the stomach and duodenum and looking dorsal to them. The duct of the 

 pancreas is somewhat difficult to find in the dogfishes, less difficult in the skate; 

 it lies imbedded in the tissue of the pancreas near the posterior margin of the 

 ventral lobe and may be exposed by picking away the pancreas tissue in this 

 region. Beyond the duodenum the intestine widens considerably, and its 

 surface is marked by parallel rings. These rings are the lines of attachment of 

 a spiral fold, the spiral valve, which occupies the interior of the intestine. (A 

 portion of the intestine often protrudes through the anus and should be pulled 

 back into the coelom by grasping the portion in the cavity and exerting a gentle 



1 It has already been explained that the organs are not in reality inside of the coelom. 



