PHYSIOLOGICAL ANATOMY OF THE SMALL LNTESTINES 2O/ 



(20.32 to 25.4 centimeters). This part of the intestine is wider than the 

 constricted pyloric end of the stomach, with which it is continuous, and 

 is also much wider than the jejunum. 



The coats of the duodenum, like those of the other divisions of the 

 intestinal tube, are three in number. The external is the serous, or 

 peritoneal coat, which has 

 already been described. 

 The middle, or muscular 

 coat is composed of non- 

 striated muscular fibres, 

 such as exist in the 

 stomach, arranged in two 

 layers. The external 

 longitudinal layer is not 

 very thick, and the direc- 

 tion of its fibres can be 

 made out easily only at 

 the outer portions of the 

 tube, opposite the attach- 

 ment of the mesentery. 

 Near the mesenteric bor- 

 der the outlines of the 

 fibres are faint. This 

 is true throughout the 

 entire small intestine, 

 although the fibres are 

 most abundant in the 

 duodenum. The internal 

 layer of fibres is consid- 

 erably thicker than the 

 longitudinal layer. These Fig> 42> ~ stomach > liver and smal1 tntestine ^ 



fiK rfl <; ^nrirrlp> f-V.^ tnl I, inferior surface of the liver ; 2, round ligament of the liver ; 



me tU DC, 3( g a n.biadder ; 4, superior surface of the right lobe of the liver ; 



running Usually at right 5, diaphragm; 6, lower portion of the oesophagus ; 7, stomach; 



i , , ,8, gastro-hepatic amentum ; 9, spleen ; 10, gastro-splenic omen- 



angles to the external tum . ^ duodenum ; 12, 12, small tntestine.- 13, ***. 14, 



layer, but SOme having an a PP endix -vermiform is ; 15, 15, transverse colon; 16, sigmoid 

 , , . JLextire of the colon ; 17, urinary bladder. 



oblique direction. The 



circular layer is thickest in the duodenum, diminishing gradually in 

 thickness to the middle of the jejunum, but afterward maintaining a 

 nearly uniform thickness throughout the canal to the ileo-caecal valve. 



The jejunum, the second division of the small intestine, is continu- 

 ous with the duodenum. It presents no well-marked line of separation 

 from the third division, but is considered as including the upper two- 



