THE DIGESTIVE SYSTEM 273 



layers, a connective-tissue stroma and mcsollu'liuin. The stroma 

 consists of loosely arranged connective-tissue bundles, which inter- 

 lace in a plane parallel to the surface. There are numerous elastic 

 fibres, especially in the deeper .'layer of the parietal peritoneum. 

 There are comparativel\- frw connective-tissue cells. The mesothe- 

 lium consists of a single layer of flat polygonal cells with bulging 

 nuclei. The cells have in^gular wavy outlines, which are easily dem- 

 onstrated with silver nwfrate (Fig. 28). The shape of the cells varies 

 considerably according to the direction in which the tissues are 

 stretched. Over some parts, e.g., the liver and intestine, the 

 peritoneum or serosa is thin and very closely attached. In places 

 where the i)u^toneum is freely movable, a considerable amount of 

 loose conn(^i\e li^|Mc, rich in elastic fibres and containing varying 

 numbers df fat ^P^ connects the peritoneum with the underlying 

 tissue. This i^Known as the "subserous tissue." The peritoneum is 

 well supplied with blood-vessels and lymphatics. The former give 

 rise to a rich capillary network. 



The mesentery is a sheet of loosely arranged connective tissue 

 covered with peritoneum. It is reflected from the p6st-abdominal 

 wall to the viscera, and serves to carry to these organs their blood- 

 vessels, lymphatics, and nerves. In the case of the stomach, duo- 

 denum, and large intestine, the mesentery is comparatively short, and 

 the organs are therefore quite firmly fixed to the abdominal wall. In 

 the case of the small intestine the mesentery is long and the intestine, 

 therefore, freely movable. The mesentery is richly supplied with lymph 

 nodes and there is usually a considerable amount of fat. From the 

 mesentery, the peritoneum, passes over to and envelops the viscera. 



The omentum (Fig. 28) is a sheet of tissue which passes from the 

 liver to the lesser curvature of the stomach (gastro-hepatic omentum) 

 to which it is attached, and from the greater curvature of the stomach 

 to the transverse colon (greater omentum) . It is similar in structure 

 to the mesentery, and contains usually much fat and many lymph 

 nodes. Its connective-tissue bundles are arranged in networks, the 

 strands and meshes of which vary greatly in size and shape. The 

 strands are covered by a single layer of mesothelium. 



Blood-vessels of the Stomach and Intestines 



The arteries reach the gastro-intestinal canal through the mesen- 

 tery, give off small branches to the serosa, and pass through the 

 muscular coats to the submucosa, where they form an extensive 



18 



