1 66 



NORMAL HISTOLOGY. 



let-cell 



.Capillary 



Cuticular border 

 of epithelium 



Lacteal 

 Vein 



Stroma of 

 mucosa 



the 

 the 

 the 



FIG. 205. Transverse section of a single villus, showing relation 

 of epithelium, stroma and vessels. X 350. 



consist of a single layer of endothelial plates and are surrounded by the 

 strands of muscle. While the absorbent vessels within the villi are at times 

 conspicuous by reason of the particles of fat which they contain, and hence 



are called ' ' lacteals, ' ' they 

 are only blind lymph- 

 radicles and actually be- 

 long to the system of 

 lymphatics. Their special 

 purpose is to carry the 

 materials taken from 

 intestinal contents to 

 great lymph-channel, 

 thoracic duct. 



The plicae circula- 

 res, or valvula conniven- 

 tes, within the duodenum 

 and jejunum, additionally 

 model the mucous mem- 

 brane and greatly increase 

 its secreting and absorbing 

 surface, as well as retard 

 the . passage of the intes- 

 tinal contents, thereby 

 facilitating the digestive 

 processes. These transverse folds begin in the second part of the duo- 

 denum and are duplicatures which involve not only the entire thickness 

 of the mucosa, but contain a central supporting projection of the submucous 

 coat (Fig. 207); hence thev can not be 

 completely effaced by distention. The 

 height of the folds, where well developed, 

 rarely exceeds 6 mm. , and towards the lower 

 part of the jejunum is much less; in the 

 terminal portion .of the ileum they usually 

 are wanting. 



Glands. The structures within the wall 

 of the intestinal tube to which the term 

 "glands" has been applied include two 

 entirely different groups the true secreting 

 organs, the glands of Brunner and the 

 crypts of Lieberkiihn, and the accumula- 

 tions of lymphoid tissue, the single or 

 aggregated lymph-nodules, which do not 

 secrete. 



The glands of Brunner or duodenal 

 glands (Fig. 208) are limited to the first 

 division of the small intestine. Beginning at 

 the pylorus, where they are most numerous 

 and extensive, they gradually decrease in 

 number and size, until, at the lower end of the duodenum, they are entirely 

 wanting. In the vicinity of the opening of the bile-duct, however, they are 

 locally augmented. These glands are direct continuations of the pyloric 

 glands of the stomach, with which they agree in all essential structural 

 details. They are not confined to the mucous coat, as are the gastric 



FIG. 206. Surface view of mucous 

 membrane of jejunum; stippled appear- 

 ance is due to villi, which cover also the 

 folds. Natural size. 



