DIGESTIVE ORGANS INTESTINES. 



529 



Fig. 230. 



volutions in the abdominal cavity. They are attached to the vertebral 

 column by folds of peritoneum called mesentery ; and according to the 

 length of these folds or duplicatures the intestine is bound down, or 

 floa,ts in the abdominal cavity. Their structure is nearly alike through- 

 out: a mucous membrane lines them: immediately without this is a 

 muscular coat; and, externally, a serous coat, formed by a prolonga- 

 tion of the peritoneum. The mucous membrane is soft and velvety, 

 and is the seat of a similar secretion to that of other membranes of the 

 same class. The muscular coat is composed of two planes of fibres, so 

 united that they cannot be separated, the innermost consisting of 

 circular, and the outermost of longitudinal fibres, the arrangement of 

 which differs in the small and large intestines. The serous or peri- 

 toneal coat receives the intestine between two of its laminse, which, 

 in their passage to it, form the mesen- 

 tery. The serous coat only comes in 

 direct contact with the intestine at the 

 sides and forepart. Behind, or on the 

 mesenteric side, is a vacant space, by 

 which the vessels and nerves reach the 

 intestine. These form their first net- 

 work between the serous and muscular 

 coats ; their second, between the muscu- 

 lar and mucous. 



Between the upper four-fifths of the 

 intestinal canal, and the lower fifth, 

 there is a well-marked distinction; not 

 only as regards structure and magnitude, 

 but function. This has given occasion 

 to a division of the canal into small 



and Tarne ivif0<iti>nt> anrl rriAP jjo-ain denum. "6. Opening of the ductus commu- 



ana large intestine, ana tnese, again, n is choiedochus into the duodenum. 

 have been subdivided in the various 



modes that will fall under consideration. As the small intestine fills 

 so large a portion of the intestinal canal, its convolutions occupy con- 

 siderable space in the abdominal cavity, 

 in the middle, umbilical, and hypo- 

 gastric regions, and terminate in the 

 right iliac region in the large intestine 

 (see Fig. 210). Its calibre differs in dif- 

 ferent parts; but it may be regarded on 

 the average as about one inch. It is 

 usually divided, arbitrarily, into three 

 parts; duodenum, jejunum, and ileum. 

 The duodenum is so called, in consequence 

 of its length having been estimated at 

 about twelve fingers' breadth. It is larger 

 than the rest of the small intestine; 

 and has received, also, the name of 

 second stomach, and of ventriculus succen- 



turiatUS. It is more firmlv fixed to the Longitudinal Section of the Upper 

 , -, ., ,, ,, . .,< , . Part of the Jejunum extended under 



body thaa the other intestines ; and does water. 

 VOL. I. 34 



Portion of the Stomach and Duodenum 

 laid open to show their interior. 



1, 1. Right, or pyloric extremity of sto- 

 mach. 2, 2. Folds and mucous follicles of 

 mucous coat of stomach. 3. Points into 

 the pylorus. 4. Thickness of the pylorus. 

 5, 5. Rugae of the internal coat of the duo- 



Fig. 231. 



