FISHERY BULLETIN: VOL. 7L NO. 2 



nerve plexus, blood vessels, and longitudinal 

 muscles merge in the connective tissue at the 

 base of the rectal valve. Some bundles of the 

 circular layer remain associated with the longi- 

 tudinal layer at the base. 



The rectum proceeds posteroventrally to the 

 anus. In the anterior part of the rectum, the 

 absorptive cells of the mucosa show more vacu- 

 oles in the supranuclear zone in well-fed speci- 

 mens. The submucosal layer has more granu- 

 locytes than the intestine. The vascular system 

 is also more prominent. The longitudinal muscle 

 layer just inside the circular layer is distinct 

 posterior to the rectal valve. Posteriorly in 

 the rectum, the number of mucous cells de- 

 creases gradually and then increases around 

 the anus. The epithelium of the rectum con- 

 tinues to the anal papillae (Figure 20). Granu- 

 locytes are the most abundant cell type in 

 both the internal folds and external papillae 

 of the anus. The circular muscle layer at the 

 end of the rectum forms a sphincterlike struc- 

 ture. The longitudinal muscles and the nerve 

 plexus radiate into the connective tissue around 

 the anus. The serosa is replaced by an ad- 

 ventitia composed of an extensive development 

 of fibrous connective tissue. 



Associated Organs 



GALLBLADDER— The gallbladder is half 

 embedded into the liver and opens anteriorly 



into the intestinal bulb via the common bile 

 duct. The bile is usually dark green and has 

 pH values between 7.5 and 8.5. The fullness 

 of the gallbladder was usually inversely cor- 

 related to the fullness of the intestine. It is 

 a highly elastic structure which becomes more 

 elongate when full. The columnar epithelial 

 cells of the mucosa have fingerlike projections 

 extending toward the lumen (Figure 17); how- 

 ever, there are no mucosal folds. A small 

 vacuolelike structure present in each columnar 

 epithelial cell of the gallbladder at the supra- 

 nuclear zone is stained intensively in fast 

 green, analine blue, and PAS preparations. 

 Rodlet cells are present and are more con- 

 centrated in the bile duct than in the bladder 

 itself (Figures 16, 17). The submucosa is a 

 rather thin layer of very dense collagenous 

 tissue in which a few granulocytes, fibrocytes, 

 lymphocytes, and capillaries are present. Smooth 

 muscle cells occur beneath the serosa, but 

 their arrangement (spiral, random, etc.) could 

 not be ascertained. The mucosa and submucosa 

 of the bile duct are similar to those of the 

 intestine; but mucous secreting cells are 

 completely absent. The rodlet cells in the bile 

 duct increase abruptly in number near its 

 entrance into the intestine. 



PANCREAS. — The pancreas is diffuse, form- 

 ing small nodules, and consists of numerous 

 small lobules scattered with fat and vascular 



Figure 20. — External surface of the 

 anal papillae of a 210-mm SL cunner 

 (X 400). a, acidophilic mucous 

 secreting cell; g, granulocyte; m, 

 basophilic mucous secreting cell; Sm, 

 submucosa. 







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