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Elementary Biology. 



away, traversing the substance of the pancreas and receiving 

 in its course ducts from that organ. The bile-duct finally 

 opens into the small intestine about midway along the re- 

 current fold. This first portion of the intestine is known as 

 the duodenum. The intestine thereafter makes a series of 



coils and finally en- 



FIG. 132. VERTICAL SECTION OF THE HUMAN -, , , . 



CESOPHAGUS. (Quain.) larges abruptly mtc 



a large short tube, 

 the rectum, which 

 opens into the cham- 

 ber already referred 

 to as the cloaca. 



The entire outer 

 surface of the ali- 

 mentary canal and 

 its glands is covered 

 by a shining mem- 

 brane continuous 

 with a similar mem- 

 brane covering the 

 inner wall of the 

 abdominal cavity, 

 and known as the 

 peritoneum. The pe- 

 ritoneum rises from 

 tfte dorsal wall of 

 the abdomen and 

 becomes continuous 

 with the layer re- 

 flected over the 

 viscera, forming na- 

 turally a double layer, which attaches the alimentary canal 

 and its glands to the abdominal wall, and forms the delicate 

 membrane known as the mesentery. The mesentery, as we 

 shall afterwards see, serves to support not only the alimentary 

 canal but also blood-vessels, ducts, and nerves. 



a, connective-tissue layer; b, longitudinal muscles, 

 cut transversely; c, circular muscles, cut longi- 

 tudinally ; d, layer containing mucous glands ; e, 

 layer of muscle fibre ; f, subepithelial tissue 

 (dermis) ; g; epithelium layer (epidermis). 



