SMALL I.VTKSTIXE. 



305 



becomes the jejunum at the level of the anterior mesenteric 

 artery. The first portion is more free than the latter. At from 

 four to five inches from the pylorus is the opening by which the 

 ducts of the liver and the pancreas enter the intestine. The 

 /' j" inini succeeds the duodenum, and includes about two-fifths of 

 the remainder of the small intestine, the ilcum constituting the 

 rest ; both are floating i.e., they are situated within the free 

 border of the mesentery. The ileum terminates, in the right 

 iliac region, in the large intestine. 



Fi,,. 100. 



The two mesenteries ; the great colon being removed, a, Anterior mesentery ; b b, Mesenteric 

 glands ; c e c, Loops of the small intestine ; d, Colic mesentery ; e e e, Loops of the floating colon ; 

 /, Sphincter ani internal layer ; g, Levator ani. 



The walls of the small intestine, in common with all hollow 

 viscera of the abdomen, consist of an external serous, a middle 

 muscular, and an internal mucous coat. The two latter are 

 joined by areolar tissue, which is sometimes regarded as a 

 submucous coat. The serous coat envelops the intestine, except- 

 ing just at its attached border, where the two folds join and form 

 the mesentery. The muscular coat consists of two layers of 

 fibres, an outer longitudinal, which is very thin, especially at the 

 attached border, and an inner circular one, which is thicker ; both 

 are pale, and involuntary. 



The mucous coat is soft, spongy, reddish, and vascular, covered 



x 



