ABDOMEN. 



243 



Yes, and the terms by which such conditions are designated are hydro-pericar- 

 dium, hydro-thorax, hydro-cephalus, and hydro-peritoneum. 



23. What is a peritoneal cavity f 



The space between the visceral and parietal layers ot the peritoneum. The 

 same is true of any serous cavity viz., it is the space between a visceral and a 

 parietal layer of serous membrane. 



24. What do we understand by mesenteric contents ? 



All the structures between the two surfaces or folds of the mesentery /. e. , 

 in the mesenteric space. The intestine is, of course, the largest structure. (Fig. 

 1 66.) The vessels, nerves, and glands to and from the intestine are all called 

 mesenteric. They are all embedded in a variable amount of mesenteric fat. 

 Sometimes this fat is so abundant as to completely hide the vessels from view ; at 

 other times the vessels may be seen. 



2 5 . Explain tlic primitive alimentary canal. 



In figure 172 you have a view of the primitive canal and its mesentery 

 in longitudinal section. Will you remember that the mesentery has two layers 



fade. U< 

 gast.Jiefiat: omcnt 



I/MES. 



FIG. 172. DIAGRAM OF THE PRIMITIVE ALIMENTARY CANAL. 



with the arteries, that make the canal grow, between them ? You see in the figure 

 only one surface of the mesentery. At an early period there is only one gut and 

 one mesentery. This gut is straight, and located in the mid-line and on the pos- 

 terior abdominal wall. The gut grows in proportion to the blood-supply it receives. 

 In figure 172 this primitive mesentery had three important organs between its 

 two layers: (i) The stomach, in the middle; (2) the liver, between the two 

 layers, in front of the stomach ; (3) the spleen, between the two layers, behind the 

 stomach. 



We see parts of this primitive partition unoccupied (i) in front of the liver; 

 (2) between the liver and stomach ; (3) between the stomach and spleen ; (4) 

 between the spleen and posterior wall. 



26. Can ive find evidence in our dissection of the unoccupied parts just referred to ? 

 Yes ; the one in front of the liver is the broad or falciform ligament of the 



liver. The one between the liver and stomach is the gastro- hepatic or lesser 

 omentum. The one between the stomach and spleen is the gastro-splcnic omentum. 



27. Give the difference between omentum and mesentery. 



