THE SMALL INTESTINE 



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of the small intestine having rolled to the left of the superior mesenteric artery, while the loops 

 which were formerly in the cord are found in the right side of the abdominal cavity. It is 

 not difficult to trace these six groups of loops through the later stages of foetal life to the new- 

 born, and thence to the adult stage. In the adult, as also through the various stages of develop- 

 ment, loop 1 forms the duodenum. From the primary groups of coils marked 2 and 3 are 

 developed the greater part of the jejunum, arranged in two distinct groups of loops, situated 

 in the left hypochondriac region. The part of the intestine developed from group 4 of the 

 primary coils passes across the umbihcal region to the right upper part of the abdomen. That 

 part developed from group 5 of the primary coils recrosses the median line to the left iliac fossa, 

 while that part derived from group 6 of the primary coils is found in the false pelvis and the 

 lower part of the abdominal cavity between the psoas muscles. (Mall.) Figs. 900, 901, 930 

 may serve to make clear these statements. They present what may be regarded as the normal 

 arrangement of the small intestine, having been found 21 times in 41 cadavers examined. 

 Variations from this arrangement occur; the great majority of such variations are, however, 

 not of sufficient importance to require special mention. 



According to Johnson (upon whose descriptions the following account is based), there is 

 in embryos of 13 mm. to 23 mm. a formation of vacuoles in the duodenal epithehum, which 



Fig. 930. — Model Showixg Course 

 OF Intestine, Made from Same Ca- 

 daver FROM WHICH Fig. 931 was Drawn. 

 (Mall.) 



Fig. 931. — The Usual Position of the 

 Intestine in the Abdominal Cavity. The 

 numbers in the figure mark the parts which are 

 homologous with the primary bends and groups 

 of coils numbered from 1 to 6. (Mall.) 



leads to complete temporary occlusion of the lumen. A persistence of this condition may cause 

 permanent atresia. In the epithelium of the small intestine numerous pockets or cysts occur, 

 which usually disappear, but may persist and form permanent diverticula or accessory pancreas. 

 The villi begin to appear at 19 mm., first in the mucosa of the upper portion of the intestine, as 

 locahzed outgrowths which become arranged in longitudinal rows. The crj-pts of Lieberkuehn 

 bud off from the epithehum at 55 mm., and from those in the duodenum, the duodenal (Brun- 

 ner's) glands begin to bud off at 78 mm. The pUcae circulares begin to appear at the mid- 

 region of the small intestuie at 73 mm. The circular muscle layer begins to appear at about 12 

 mm., the longitudinal at 75 mm. 



Variations in the small intestine. — Although relatively fixed in position, the duodenum 

 is quite variable in form. The C-shap*^ previously described is the most common. When 

 the pylorus and the duodeno-jejunal flexure are approximated, the form is nearly circular. 

 When the two ends are more widely divergent, it approaches a U-form. Not infrequently, 

 the inferior portion ascends abruptly from the inferior angle, giving a V-form. Finally, the 

 terminal ascending portion may be very small or absent, in which case the duodenum ap- 

 proaches an L-form. Variations in the position of the various coils of the jejunum and ileum 

 have already been discussed. The lymph-nodules, including Peyer's patches, like all lym- 

 phoid structures, are prominent during youth, but become atrophied in old age. 



Meckel's diverticulum, which represents a derivation from the embryonic yolk stalk and 

 sac, is found in about 2 per cent, of all adults. It is a bhnd tube or diverticulum of variable 



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