456 DISSECTION OF THE ABDOMEN. 



network in the fibrous layer. Both sets leave the stomach with the 

 bloodvessels. 



Nerves. The nerves are derived from the pneumo-gastric and sympa- 

 thetic (p. 451), and can be followed to the fibrous coat; small ganglia 

 have been observed on them. 



SMALL INTESTINE. 



The three parts into which the small intestine is divided, have the fol- 

 lowing characters : 



The duodenum measures as much as the breadth of twelve fingers, viz., 

 about ten inches, and is more fixed than the rest of the intestinal tube. 

 It is wider than either the jejunum or the ileum, and its muscular coat is 

 also thicker. Into it the common bile and pancreatic ducts pour their 

 contents. 



The jejunum and the ileum together measure about twenty feet in 

 length, and are connected with the mesentery. There is not any percep- 

 tible difference between the termination of the one and the commencement 

 of the other, but two-fifths of the length are assigned to the jejunum, 

 and three-fifths to the ileum. Between the ends, however, a marked dif- 

 ference may be perceived ; for the upper part of the jejunum is thicker 

 and more vascular than the lower part of the ileum, and its width is also 

 greater. 



STRUCTURE. In the small intestine the wall is formed by the same 

 number of layers as in the stomach, viz., serous, muscular, fibrous, mucous, 

 and submucous. 



Dissection. The different layers are to be examined on pieces, about 

 three inches long, taken from the duodenum, the upper part of the jejunum, 

 and the lower end of the ileum. After the pieces have been cut off, they 

 are to be distended with air ; and the serous covering is to be torn off for 

 a short distance, to show the muscular coat, but in doing this, the external 

 longitudinal fibres will be taken away without great care. 



The serous coat is closely connected with the subjacent muscular layer. 

 To the jejunum and ileum it furnishes a covering, except at the attached 

 part where the vessels enter : at this spot the peritoneum is reflected off to 

 form the mesentery, and a space exists resembling that at the borders of 

 the stomach. The peritoneum surrounds the duodenum only partly; this 

 peculiarity has been described at p. 438. 



The muscular coat is constructed of two sets of fibres, a superficial or 

 longitudinal, and a deep or circular. The fibres are pale in color, and are 

 not striated. 



The longitudinal fibres form a thin covering, which is most marked at 

 the free border of the gut. 



The circular fibres are much more distinct than the others, and give 

 the chief strength to the muscular coat : they do not form complete rings 

 around the intestine. 



Dissection. On the removal of a part of the muscular stratum from 

 the jejunum or the ileum, the submucous fibrous layer will come into view. 



The fibrous coat has the same position and use as the corresponding 

 layer in the stomach. 



Dissection. In the upper part of the duodenum the student is to seek 

 some small compound glands those of Brunner, which are imbedded in 

 the submucous tissue. They lie beneath the mucous membrane, and will 



