166 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



also called the lesser omenlum. It may be roughly divided into two portions, the 

 hepatoduodenal ligament extending from the liver to the duodenum and contain- 

 ing the bile duct and blood vessels, and the gastrohepatic ligament extending 

 from the stomach to the liver and duodenum and in the dogfishes occupying also 

 the angle formed by the bend of the stomach. Another remnant of the ventral 

 mesentery is the suspensory or falciform ligament of the liver. This will be 

 found at the anterior end of the liver, extending from the mid ventral surface 

 of the liver to the midventral line of the body wall. In mature females the 

 mouth of the oviduct will be noticed in the falciform ligament as a funnel-shaped 

 aperture. After seeing the falciform ligament the flap of body wall left in the 

 skate may be cut off. 



Each gonad has a mesentery which is a special fold arising from the dorsal 

 wall very near the origin of the dorsal mesentery. The mesentery of the ovary 

 is called the mesovarium, of the testis, the mesorchium. In the case of mature 

 females, each oviduct has also a mesentery, the mesotubarium. 



The anterior end of the pleuroperitoneal cavity will be found closed by a 

 partition, the transverse septum, the posterior face of which is clothed by the 

 parietal peritoneum. The liver is attached to the septum by the strong coronary 

 ligament which is, in fact, a portion of the septum. In its early development the 

 liver is inclosed in the transverse septum, and subsequently, because of increased 

 size, projects posteriorly from the septum which then narrows around the anterior 

 end of the liver and forms the coronary ligament (see Fig. 48, p. 195). 



The pleuroperitoneal cavity communicates with the exterior by means of 

 the abdominal pores. These will be found one on each side of the anal opening 

 (in the skate posterior to the anus) somewhat concealed by a fold of skin. Probe 

 into them and note that they lead into the pleuroperitoneal cavity. Their 

 purpose is obscure. 



The pleuroperitoneum is the lining of the hypomere and the pleuroperitoneal cavity is 

 the cavity of the hypomere. The pleuroperitoneal membrane is divided into three regions, 

 according to its relations to other structures: first, the parietal peritoneum, that portion of the 

 membrane lining the inner surface of the body wall; second, the visceral peritoneum, forming 

 the thin outer covering of all of the viscera; and third, the mesenteries or ligaments, portions 

 of the membrane extending from the body wall to the viscera or from one viscus to another. 



Draw the contents of the pleuroperitoneal cavity. Make a diagram of an 

 imaginary section through the anterior end of the pleuroperitoneal cavity, show- 

 ing gonads, stomach, and liver, and the relations of the pleuroperitoneum to 

 them and to the body wall. 



4. The pericardial cavity. Make an incision through the skin in the median 

 ventral line from the pectoral girdle up to the lower jaw. Leave the girdle 

 intact. Gently strip off with a forceps the layers of visceral muscle until you 

 have exposed a membrane. This membrane is the parietal pericardium. Slit 

 open this membrane and see that it incloses a cavity, the pericardial cavity, in 



