STRUCTURE OF MUCOUS MEMBRANE. 507 



surface of the membrane, and the bases forming by their approxi- 

 mation the free intestinal surface. Each column is provided with a 

 central nucleus and nucleus-corpuscle, which gives to its middle a 

 swollen appearance ; and, from the transparency of its structure, 

 the nucleus may be seen through the base of the column, when ex- 

 amined from the surface. Around the circular villi the columns, 

 from being placed perpendicularly to the surface, have a radiated 

 arrangement. The columnar epithelium is produced in the same 

 manner with the laminated epithelium, in nuclei, vesicles, and co- 

 lumns, and the latter are continually thrown off to give place to 

 successive layers. 



The Proper mucous, or Papillary layer is analogous to the papil- 

 lary layer of the skin, and, like it, is the secreting structure by 

 which the epithelium is produced. Its surface presents several 

 varieties of appearance when examined in the different parts of its 

 extent. In the stomach it forms polygonal cells, into the floor of 

 which the gastric follicles open. In the small intestine it presents 

 numerous minute, projecting papillae, called villi. The villi are of 

 two kinds, cylindrical and laminated, and so abundant as to give to 

 the entire surface a beautiful velvety appearance. In the large in- 

 testine the surface is composed of a fine network of minute polygo- 

 nal cells, more numerous than those of the stomach, but resembling 

 them in receiving the secretion from numerous perpendicular folli- 

 cles into their floors.* 



The Fibrous layer (submucous, nervous) is the membrane of 

 support to the mucous membrane, as is the corium to the papillary 

 layer of the skin. It gives to the mucous membrane its strength 

 and resistance, is but loosely connected with the mucous layer, but 

 is firmly adherent to the muscular stratum, and is called, in the 

 older works on anatomy, the " nervous coat." 



In the loose cellular tissue connecting the mucous with the fibrous 

 layer, are situated the glands and follicles belonging to the mucous 

 membrane : these are the 



Pharyngeal glands, 



CEsophageal glands, 



Gastric follicles, 



Duodenal glands, (Brunner's), 



Glandular solitaria?, 



Glandulae aggregatae (Peyer's), 



Simple follicles (Lieberkiihn's). 



The Pharyngeal 'glands are situated in considerable numbers 

 beneath the mucous membrane of .the pharynx, particularly around 

 the posterior nares. Two of these glands, of larger size than the 



* The first notice of the true structure of mucous membrane appeared in the 

 American Journal of Medical Sciences, and was from the pen of Professor Horner. 

 The preparations which he made at the time are in the Wistar Museum, and illustrate 

 the structure beautifully. G. 



