368; DR D. BEREY HART. 



answer to this involves some questions of development which we 

 must now recapitulate. 



(2) The dcvelo^mient of the anus and of the 2)re2)n.ce of the 

 clitoris and 2Tcnis. — -The lining of the rectum is a hypoblastic 

 structure, while that of the anus is epiblastic. In the three and 

 a half months' fostus one can see the epidermis passing in at the 

 anal site, and at the top of the anus gradually passing into that 

 of the Lieberkiihnian follicles (fig. 19). The superficial cells 

 of the epidermis so passing in are necessarily central, and as 

 they desquamate, form the lumen. 



The views advanced by embryologists as to the development 

 of the prepuce are discordant, and in some respects unintelli- 

 gible. Milnes Marshal], for instance, says : " The prepuce appears 

 towards the end of the third month as a fold of skin round the 

 base of the glans, and is at first interrupted ventrally by the 

 urethral groove" (p. 597, 1893). Minot (pp. 517-9, edit. 1897) 

 gives two accurate, though rather ill-defined drawings, and 

 says : " The prepuce appears as a slight ridge whicli overgrows 

 the glans, the epithelium of the inner surface uniting as the 

 fold blends with the epithelium of the glans — the two epithelia 

 fusing into one solid plate." 



"With this description I disagree, and the account I urge as a 

 more correct one is already given at page 339. 



There is thus a close parallel between this development of the 

 prepuce and that of the vaginal lining. The vaginal lining 

 is derived from the Wolffian bulbs, and they render the previous 

 Milllerian lumen of the vagina solid, and when central des- 

 quamation takes place a fresh lumen is formed. The Wolffian 

 bulbs are of course epiblastic in origin (vide p. 341). 



To understand the difference in behaviour of the mucous 

 membranes when exposed to pressure, we must remember their 

 origin. The so-called mucous membranes of the inner surface 

 of the prepuce, anus, and vagina are epiblastic in origin, and 

 revert to epidermis when eversion is permanent. They »hould 

 be thus classed as epiblastic mucous membranes or muco- 

 cutaneous surfaces (Turner). Eectal mucous membrane, on the 

 other hand, is hypoblastic in origin, is a true mucous membrane 

 with a mucous secretion, and takes on no squamous character 

 when everted permanently. 



