310 DIGESTION. 



it is about the length of the breadth of twelve fingers, i. e., 

 from eight to ten inches. This portion of the intestine is 

 considerably wider than the constricted pyloric end of the stom- 

 ach, with which it is continuous, and is also much wider than 

 its continuation, the jejunum. It presents a curve, which is 

 ordinarily described by anatomists as consisting of three por- 

 tions. The first, called the hepatic or ascending portion, is 

 about two inches in length. This is much less firmly fixed 

 by its peritoneal attachment than the other portions, and is 

 nearly covered by the serous membrane. Its direction is 

 outward, backward, and slightly upward. Turning down- 

 ward, and a little inward, it merges into the second, called 

 the descending or vertical portion, the length of which is 

 about three inches. This is covered with peritoneum only on 

 its anterior surface, and is somewhat more firmly attached 

 than the ascending portion. The intestine then makes a sec- 

 ond bend, and the third or the transverse portion is 

 horizontal in its course, passing across the spine into the left 

 hypochondrium. This portion is about five inches in length. 

 It is narrower than the others, is but partially covered by 

 peritoneum, and is more firmly bound down than any other 

 part of the small intestine. 



The coats of the duodenum, as of the other divisions of 

 the intestinal tube, are three in number. Commencing ex- 

 ternally, we have the serous, or peritoneal coat, which has 

 already been described. The middle, or muscular coat, is 

 composed of the involuntary or unstriped muscular fibres, 

 such as exist in the stomach, arranged in two layers. The 

 external, longitudinal layer is not veiy thick, and the direc- 

 tion of its fibres can be made out easily, only at the outer 

 portions of the tube, opposite the attachment of the mesen- 

 tery. Near the mesenteric border, the fibres are very faint. 

 This is true throughout the whole of the small intestine ; 

 though the fibres are most numerous in the duodenum. The 

 internal, circular, or transverse layer of fibres is considerably 

 thicker than the longitudinal layer. These fibres encircle 



