THE SMALL INTESTINE. 



367 



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pyloric end of the stomach, the mucous mem]_)vane is seen projecting in 

 the form of a circular fold, called the pylorus, leaving a correspondingly 

 narrow opening <%. 2G6, })). Within this fold are circular muscular 

 fibres, belonging to the 

 general system of circular 

 fibres of the alimentary 

 canal, which are here col- 

 lected in the form of a 

 strong band, whilst the lon- 

 gitudinal muscular fibres 

 and the peritoneal coat pass 

 over the pyloric fold to the 

 duodenum, and do not enter 

 into its formation (fig. 253). 

 Externally the pylorus may 

 be easily felt, like a thick- 

 ened ring, at the right end' 

 of the stomach, where also 

 a slight external constriction 

 is visible. Internally its 

 opening is usually circular 

 and less than half an inch 

 across, so that it is the 

 narrowest part of the whole 

 alimentary canal. 



Occasionally the orifice is 

 oval, and it is often placed a 

 little to one side. Sometimes 

 the circular rim is imperfect, 

 and there are found instead 

 two crescentic folds, placed one 



above and the other below the passage (Huschke) ; and, lastly, there is occasion 

 ally but one such creecentic fold. 



Fig. 251. — Lymphatics of thr Hu.man Gastric 

 ilucous Mejibkane, Injected (from Loven). 



The tubules are only faintly indicated ; a, muscu- 

 laris mucosae ; h, plexus of fine vessels at base of 

 glands ; c, plexus of larger, valved lymphatics in 

 submucosa. 



THE SMALL IINTESTIITE. 



The small intestine (fig. 252, D, j, i) commences at the pylorus, 

 and after many convolutions terminates in the large intestine. It 

 measures on an average about twenty feet in length in the adult, 

 and gradually becomes slightly narrower from its upper to its lower 

 end. Its convolutions occupy the* middle and lower part of the 

 abdomen, and are surrounded by the large intestine. They are con- 

 nected 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 tea or twelve inches im- 

 mediately succeeding to the stomach, and comprehending the widest 

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

 tv\o-fifths of the remainder being named the jejunum, and the lower 

 three-fifths the iJcwn. There are no distinct lines of demarcation 

 between these three parts, but there are certain peculiarities of connec- 

 tion and certain diiterences of internal structure to be observed in 



