406 THE SOLIDS. 



Independent of the important differences indicated in the 

 preceding paragraph, there are others, viz. the larger size of 

 the follicles of the mucous glands and the coarser and firmer 

 texture of the membrane which constitutes their parietes. 



That the follicles do really communicate with each other 

 is proved by the numerous circular apertures which they fre- 

 quently present, and which reminds one of those of the air- 

 cells of the lungs. (Plate LIILjfy. 4.) 



The epithelium contained within the follicles is very small, 

 the majority of the cells being spherical. 



The membrane of the follicles would appear to be fibrous, 

 and is sufficiently resisting to preserve their form under or- 

 dinary pressure and manipulation. 



These glands have been already referred to under the 

 head of mucous glands, with which they are structurally 

 identical. 



I was led, for a short time, into the error of arranging them 

 with the tubular glands, in consequence of observing that each 

 of the larger glands of Brunner was generally furnished with 

 several tubular ducts ; and this led me at first to infer that 

 they were formed entirely upon the tubular type, which is 

 not the case. 



In those instances in which more than one duct proceeds 

 from what appears to be a single gland, this gland is not 

 really simple, but compound ; that is to say, it is formed of 

 several clusters of follicles held together by fibrous tissue, 

 and from each of which a separate efferent duct proceeds. 



The glands of Brunner occur only in the duodenum, and 

 occupy usually the upper two thirds of that intestine : their 

 number and extent of distribution vary, however, in dif- 

 ferent subjects. 



For further particulars, see the description of the (( Mucous 

 Glands." 



