668 ORGANS OF DIGESTION. 



Vessels and Nerves. The arteries supplying the duodenum are the pyloric 

 and pancreatico-duodenal branches of the hepatic, and the inferior pancreatico- 

 duodenal branch of the superior mesenteric. The veins terminate in the gastro- 

 duodenal and superior mesenteric. Its nerves are derived from the solar 

 plexus. 



The jejunum (jejunus, empty), so called from being usually found empty after 

 death, includes the upper two-fifths of the rest of the small intestine. It com- 

 mences at the duodenum on the left side of the second lumbar vertebra, and 

 terminates in the ileum; its convolutions being chiefly confined to the umbilical 

 and left iliac regions. The jejunum is wider, its coats thicker, more vascular, 

 and of a deeper color than those of the ileum ; but there is no characteristic 

 mark to distinguish the termination of the one, or the commencement of the 

 other. 



The ileum (txtv, to twist), so called from its numerous coils or convolutions, 

 includes the remaining three-fifths of the small intestine. It occupies chiefly the 

 umbilical, hypogastric, right iliac, and occasionally the pelvic, regions, and ter- 

 minates in the right iliac fossa by opening into the inner side of the commence- 

 ment of the large intestine. The ileum is narrower, its coats thinner and less 

 vascular than those of the jejunum; a given length of it weighing less than the 

 same length of jejunum. 



Structure of the small intestine. The wall of the small intestine is composed of 

 four coats ; serous, muscular, cellular, and mucous. 



The serous coat is derived from the peritoneum. The first or ascending por- 

 tion of the duodenum is almost completely surrounded by this membrane ; the 

 second or descending portion is covered by it only in front ; and the third or 

 transverse portion lies behind the descending layer of the transverse mesocolon, 

 by which it is covered in front. The remaining portion of the small intestine is 

 surrounded by the peritoneum, excepting along its attached or mesenteric border ; 

 here a space is left for the vessels and nerves to pass to the gut. 



The muscular coat consists of two layers of fibres, an external or longitudinal, 

 and an internal or circular layer. The longitudinal fibres are thinly scattered 

 over the surface of the intestine, and are most distinct along its free border. 

 The circular fibres form a thick, uniform layer ; they surround the cylinder of 

 the intestine in the greater part of its circumference, but do not form complete 

 rings. The muscular coat is thicker at the upper, than at the lower part of the 

 small intestine. 



The cellular or wbmucotu coat connects together the mucous and muscular 

 layers. It consists of a loose, filamentous, areolar tissue, which forms a nidus for 

 the subdivision of the nutrient vessels, previous to their distribution to the mucous 

 surface. 



The mucous membrane is thick and highly vascular at the upper part of the 

 small intestine, but somewhat paler and thinner below. It presents for examina- 

 tion the following constituents : 



^ -.-. -i- Simple follicles. 



Jiipitnelium. / -TV i 11 



T7 - r T T ( Duodenal glands. 



Valvula3 conniventes. ni ^ ) v* r j 



-y-n- (jrlauds. < solitary glands. 



( Agminate or Peyer's glands. 



The epithelium,, covering the mucous membrane of the small intestine, is of 

 the columnar variety. 



The valvulse conniventes (valves of Kerkring) are reduplications or foldings 

 of the mucous membrane and submucous tissue, containing no muscular fibres. 

 They extend transversely across the cylinder of the intestine for about three- 

 fourths or five-sixths of its circumference. The larger folds are about two inches 

 in length, and two-thirds of an inch in depth at their broadest part ; but the 

 greater number are of smaller size. The larger and smaller folds alternate with 

 each other. They are not found at the commencement of the duodenum, but begin 



