OF THE MUCOUS MEMBRANE. 193 



momentary folds, in which the mucous membrane is in re- 

 serve for future dilatations of the organs, or, which depend 

 upon the expansion and subsequent contraction of the organ, 

 by which the mucous membrane is made to exceed the mus- 

 cular membrane: such are the longitudinal wrinkles of the 

 oesophagus and trachea, the irregular wrinkles of the stomach 

 when contracted, the regular wrinkles of the vagina and of 

 the neck of the uterus, &c. 



264. The free surface of the mucous membrane presents 

 also cavities or depressions of various kinds, and papillary 

 and villous projections. But these various objects, although 

 generally dispersed throughout the membrane, do not exist, 

 or at least are not equally apparent in all points of its extent. 

 Infundibuliform cellular or alveolar depressions are found on 

 the surface of the membrane: they are found at the maximum 

 of their development in the second stomach of the ruminantia, 

 which on this account is called the honeycomb; they exist also, 

 but much smaller and more microscopical, in a great part of the 

 alimentary canal, and particularly in the oesophagus, stomach, 

 and the colon of man, where they were perceived and pointed 

 out by Fordyce and Hewson, and described and figured by 

 M. Ed. Home. 



265. The follicles* only differ from these alveolar depres- 

 sions in having a very small orifice, a neck more or less pro- 

 longed, and a bottom resembling an ampulla, placed in the 

 sub-mucous tissue where they project. They are formed by 

 a reflection of the membrane, strengthened externally by- 

 dense cellular tissue, and provided with numerous small ves- 

 sels. They are every where to be found, their number, how 

 ever, varies according to the part ; they are, in general, very 

 small, but they vary also greatly in size. Some are simple 

 and separate; others terminate in a common canal of which 

 they arc as it were branches; others again end in a common 

 and dilated orifice, called a lacuna; such is the hole at the base 

 of the tongue, the Iacuna3 of the urethra, rectum, &c.; another 



* Peyer. dc Gltmdulis intestinalium. Amstel. 1681. T. C. Brunner. dc 

 Glandulis duodeni. Francof. 1715. 



