THE DIGESTIVE TRACT. 





I/I 



Longitudinal section of large intestine of child : a, 

 a, simple tubular glands ; b, submucous tissue ; c and 

 d, circular and longitudinal layers of muscle. 



FIG. 211. 



conversion into goblet-cells. Lieberkiihn's glands lie between the 

 bases of the villi, but are found 



upon the valvulae conniventes, FIG- 210. 



since the latter depend on the 

 elevation of the submucosa for 

 their formation, the mucosa 

 being reflected over the pro- 

 jecting underlying tunic. In 

 the lower part of the large in- 

 testine the glands of Lieber- 

 ktihn increase in size, becom- 

 ing longer and possessing 

 wider mouths, their orifices 

 appearing as minute pits. 



The duodenum, especially in its upper part, possesses an additional 

 layer of true secreting 

 structures in the glands of 

 Brunner. These are the 

 direct continuations and 

 higher specializations of 

 the pyloric glands of the 

 stomach. In passing from 

 the stomach into the intes- 

 tine these tubules undergo 

 repeated division, and, at 

 the same time, sink deeper 

 and deeper into the mu- 

 cosa, finally reaching below 

 the limits of this layer to 

 take up a position within 

 the submucosa of the duo- 

 denum, beneath the over- 

 lying layer of the follicles 

 of Lieberkiihn within the 

 mucosa. 



Brunner's glands, or 

 the duodenal glands, 

 appear as groups of short, 

 wide, tubular acini, dis- 

 posed about long, slender 

 ducts which pass from the Section of duodenum of cat ; ^ mucosa containing the 



SUbmUCOUS tissue through villi (/) and the follicles of Lieberkuhn (/ ), and pierced by 



the mucosa to open on the the ducts ( ^ of the g , lands of Brunn J <*> with ; n the .' ub - 



l mucosa (c) ; 6, musculans mucosa: ; d, <?, circular and Ion- 



intestinal Surface between gitudinal layers of muscle ; e, fibrous tunic. 



