THE ALIMENTARY CANAL AND ITS APPENDAGES, 339 



orifice and narrows it. This is due to a thick ring of the 

 circular muscular layer there developed, and forming around 

 the orifice a sphincter muscle, which, by its contraction, keeps 

 the passage to the small intestine closed except when portions 

 of food are to be passed on from the stomach to succeeding 

 divisions of the alimentary canal. 



Since the cardiac end of the stomach lies immediately be- 

 neath the diaphragm, which has the heart on its upper side, 

 its over-distension, due to indigestion or flatulence, may im- 

 pede the action of the thoracic organs, and cause feelings of 

 oppression in the chest, or palpitation of the heart. 



The Small Intestine (Fig. 1*20), commencing at the py- 

 lorus, ends, after many windings, in the large. It is about six 

 meters (twenty feet) long, and about five centimeters (two 

 inches) wide at its gastric end, narrowing to about two thirds 

 of that width at its lower portion. Externally there are no 

 lines of subdivision on the small intestine, but anatomists 

 arbitrarily describe it as consisting of three parts; the first 

 twelve inches being the duodenum, D, the succeeding two 

 fifths of the remainder the jejunum, J, and the rest the 

 ileum, I. 



Like the stomach, the small intestine possesses four coats 3 

 a serous, a muscular, a submucous, and a mucous. The! 

 serous coat is formed by a dup'licature of the peritoneum, but 

 presents nothing answering to the great omentum; this 

 double fold, slinging the intestine as the small omenturn 

 slings the stomach, is named the mesentery. The muscular 

 coat is composed of plain muscular tissue arranged in two 

 strata, an outer longitudinal, and an inner transverse or cir- 

 cular. The submucous coat is like that of the stomach; con- 

 sisting of loose areolar tissue, binding* together the mucous 

 and muscular coats, and forming a bed in which the blood 

 and lymphatic vessels (which reach the intestine in the fold 

 of the mesentery) break up into minute branches before en- 

 tering the mucous membrane. 



The Mucous Coat oFthe Small Intestine. This is pink, 

 soft and extremely vascular. It does not present temporary 

 or effaceable folds like those of the stomach, but is, through- 

 out a great portion of its length, raised up into permanent 

 transverse folds in the form of crescentic ridges, each of 

 which runs transversely for a greater or less way round the 

 tube (Fig. 114). These folds are the valvulce connivences. 



