OP THE MUCOUS MEMBRANE. 197 



which are still more frequently observed in the same parts in 

 a form called warts. 



The existence of the epidermis is much more manifest, with- 

 out, however, being general. 



272. The epidermis or epithelium is very apparent at the 

 orifices of the mucous cavities; it is less so in their deeper 

 parts, and finally ceases to be apparent. Does it however 

 exist there? Haller and others have thought that it does, 

 and that the accidental membraniform excretions are a proof 

 of it. Every pathologist of the present day, knows that such 

 excretions are generally the result of a plastic inflammation, 

 and sometimes of eschars. The same conclusion has been at- 

 tempted to be drawn from the formation of an artificial anus, 

 accompanied with a retroversion of the intestine in which the 

 epidermis becomes very apparent; but this only proves that 

 the free surface of the mucous membrane is covered with a 

 substance which is very analogous to the epidermis, and which 

 is very much disposed to undergo this transformation. By 

 depending upon what observation teaches, and, by the use of 

 dissection, decoction and putrefaction, to separate the epithe- 

 lium, it is found very distinct as far as into the esophagus, ter- 

 minating suddenly at the union of this canal with the stomach; 

 it is also very distinct in the vagina, terminating all at once 

 on the lips of the os uteri, interruptions long ago known, 

 and erroneously adduced by some modern writers as proofs 

 of the interruption of the mucous membrane itself. In 

 other parts, as in the nasal fossae and the inferior extremity 

 of the alimetary canal, their diminution of the appearance of 

 the epithelium is gradual, insensible, and it is impossible to 

 assign its limits with exactness. In those places where it is 

 distinct, it dips, becoming thinner and thinner, into the folli- 

 cles, where it is lost. In places deprived of a distinct epithe- 

 lium, the free surface of the membrane is covered with a 

 mucous varnish, which from the time of Vesalius and even 

 of Rhazes, has been compared to the covering or tinning of 

 vessels; and of which Glissen has remarked, at least with re- 

 gard to its functions, the analogy with the epidermis. 



273. The cellular tissue which forms the corium of the 



