CHAPTER IX. 



THE INTESTINAL CANAL AND ITS SECRETION. THE 

 INTESTINAL JUICE OR SUCCUS ENTERICUS. 



SECT. 1. INTRODUCTORY OBSERVATIONS ON THE STRUCTURE OF 

 THE INTESTINAL TUBE. 



The Small Intestine. 



THE small intestine is a convoluted tube which commences at the 

 pylorus and ends in the large intestine or colon, the opening between 

 the two being guarded by the so-called ilio-ccecal or ilio-colic valve. 

 " Its convolutions occupy the middle and lower part of the abdomen 

 and are surrounded by large intestine. They are connected with the 

 back of the abdominal cavity and are held in their position by a fold 

 of the peritoneum, named the mesentery, and by numerous blood- 

 vessels and nerves." 



" The small intestine is arbitrarily divided into three portions, 

 which have received different names ; the first ten or twelve inches 

 immediately succeeding to the stomach and comprehending the 

 widest and most fixed part of the tube, being called the duodenum, 

 the upper two-fifths of the remainder being named the jejunum, and 

 the lower three-fifths the ileum. There are no distinct lines of 

 demarcation between these three parts, but there are certain pecu- 

 liarities of connections and differences of internal structure to be 

 observed in comparing the upper and lower ends of the entire 

 tube 1 ." 



The intestine, small and large, throughout its length from the 

 pylorus to close upon the rectum, possesses the general arrangements 

 of structures which characterise the whole alimentary canal. "A 

 thin outer longitudinal muscular layer, covered by peritoneum, is 

 succeeded by a thicker inner circular muscular layer, and this double 

 muscular coat is separated, by a submucous layer of loose connective 

 tissue, carrying the large blood-vessels, from the mucous membrane ; 

 the latter consists of an epithelium lying upon a connective tissue 

 basis of a peculiar nature. A well-developed muscularis mucosce, 



1 Quain's Anatomy, 9th ed. Vol. n. p. 599. 



