THE ALIMEXTAEY TRACT. 287 



greater part of the stomach, is, in the normal condition, under cover 

 of the liver (Figs. 185, 194): while under the liver the intestine 

 is firmly attached to the deep surface of that organ by a short 

 but strong Ligamentum Tiepato-dv.culenah', it then turns suddenly 

 backwards, increases in size, and by means of numerous convo- 

 lutions occupies a considerable portion of the right half of the 

 abdomen (Fig. 1 84 If}. It is held in position by a well-developed 

 mesentery. 



b. Minute structure. Like other portions of the alimentary 

 canal, the small intestine is formed of four layers : 



1 i ) The serous coat presents no peculiarities ; it consists simply 

 of a layer of endothelial cells, with a small amount of sub-endothe- 

 lial connective-tissue. 



(2) The muscular coat is in two layers, the outer longitudinal 

 layer being very thin, the inner circular layer thick. 



(3) The submucous layer resembles that of the stomach, but is 

 not so thick ; the ni>i*fii?ar'i$ mi' coxae is well developed and arranged, 

 as in the stomach, in two layers. 



(4) The mucous coat i Fig. 189) is thrown into folds, which differ 

 in various parts of the tube. 



The longitudinal folds of the stomach are compressed together 

 towards the pyloric end of the stomach (a) and diminish in size; at 

 the commencement of the duodenum they end abruptly (a 1 ), but 

 without any indication of a valvular arrangement. 



Immediately beyond the pylorus the mucous membrane is folded 

 so as to form an irregular network of folds which inclose irregular 

 alveoli; the folds are thicker on the concave surface of the duo- 

 denum, and form a longitudinal ridge (b]; in this ridge the 

 alveolar spaces are much smaller than those to either side. The 

 irregular folding extends through two to three cm., when a more 

 regular arrangement commences in the form of two adjacent series 

 of transverse folds (c, c 1 ). Each fold is semi-lunar in shape, with 

 the convexity attached to the wall of the tube and directed forwards, 

 while the concave free border and pocket-like space enclosed are 

 directed backwards. 



The arrangement of these folds reminds one of the semi-lunar 

 valves of the human heart, and probably one of their functions is 

 to prevent the regurgitation of the chyme (Wiedersheim). 



The corresponding- valves of opposite sides meet at each end at 

 an angle, the apex of which is directed away from the stomach. On 



