THE DIGESTIVE TRACT. 



171 



Lieberkiihn's glands lie between the 



FIG. 210. 



a, simple tubular glands ; b, submucous tissue ; 

 d, circular and longitudinal layers of muscle. 



conversion into goblet-cells, 

 bases of the villi, but are found 

 upon the valvulae conniventes, 

 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- 

 kiihn 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 FlG - 2I1 - 



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 stibmucosa 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 : a, mucosa containing the 



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



the niUCOSa tO Open On the the ducts ^ of the S lands of Brunner (A) within the mu- 

 - cosa (c) ; b, muscularis mucosa; ; d, d 1 , circular and lon- 



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



