MORPHOLOGY OF THE HUMAN URIXOGENITAL TRACT. 367 



- VIII. On THE Nature and Development of Mucous 



Membranes. 



There is admitted difficulty in defining what we mean by 

 ' mucous membrane'; and Bland Sutton states that practically 

 there is no difference between skin and mucous membrane. 

 Hair, he believes, can grow on mucous membrane ; and in his 

 work on Dermoids he considers the Graafian follicles as 

 practically mucous follicles — i.e., with the power of producing 

 skin products. 



A s-tudy of the development of the prepuce of the clitoris 

 and penis, and of the development of the permanent lining of 

 the vagina, seems to me to throw some light on this question, 

 and therefore I purpose to consider it at this stage. I accord- 

 ingly consider — 



(1) The behaviour of mucous membranes when everted. 



(2) The develo23ment of the anus and of the prepuce of the 



clitoris and penis. 



(1) The behaviour of mucous membranes when everted. — The 

 gynaecologist has good opportunity of observing this in certain 

 clinical cases. Thus, in prolapsus uteri and in tears of the 

 perineum sufficiently extensive to involve the anus and rectum, 

 he can observe how the exposed mucous membranes alter or 

 remain moist when exposed to unusual friction or irritation. 



The vaginal lining is generally described as mucous membrane, 

 although many consider it as more correctly presenting greater 

 affinity to skin. In the natural condition its free surfaces are 

 moist and rose-coloured, but when these are everted, as in 

 prolapsus uteri, they take on all the dryness and appearance of 

 ordinary skin. The same holds good for the glans penis after 

 circumcision. In marked contrast with this is the condition of 

 the rectal mucous membrane in complete anal tear. Here the 

 everted mucous membrane of the rectum retains its fresh red 

 colour and moisture, and never approximates in appearance to 

 skin. The anal lining, however, is hardly distinguishable from 

 skin. All I hese surfaces are, however, indiscriminately classed 

 as mucous membranes, although their behaviour under altered 

 conditions of friction and pressure is so different ; and the ques- 

 tion may be asked, What is it that makes the difference ? The 



