1S4 GENERAL ANATOMY. 



in the adult we see the skin easily transformed into mucous 

 membrane, and the latter into skin. When, for example, B 

 part of the surface of the body, is for a long time substracted 

 from the action of the atmosphere, as has been seen in cases 

 of contractions, where the leg has been strongly flexed upon 

 the thigh, as is often seen in the furrows of the skin of very 

 fat children, the epidermis softens and disappears, and the skin 

 at last secretes mucus. In a prolapsus of the uretus, on the 

 contrary, we see the mucous membrane of the vagina, and in a 

 prolapsus of the anus, natural or accidental, that of the rectum, 

 thicken, dry and assume the appearance of the skin. Finally, 

 in a healthy state, in many parts, we see the skin change into 

 mucous membrane gradually and insensibly; this is the case 

 in the labia pudendi, the prepuce, anus, mammae, and nostrils; 

 it is only in the eyelids and lips that the line of demarcation 

 appears somewhat defined. There is then no real interruption, 

 but, on the contrary, there is a perfect identity and continuity 

 between the two principal parts of the tegumentary mem- 

 brane. 



244. The various parts of these two principal portions of 

 the tegument, present also tolerably great differences. Those 

 which are observed between the skin of the back and that of 

 the eyelids, between those of the cranium and of the papillary 

 extremities of the fingers, for instance, are tolerably great, but 

 the} 7 are neither absolute nor definite; it is about the same in 

 the mucous membrane, and the interruptions which have been 

 supposed to be found there, are merely apparent, as will be seen 

 hereafter, (sec. ii.) The differences that are observed between 

 the various parts of the mucous membrane, although more 

 strongly marked than those which are found in the skin, are 

 not more real. The change of appearance and texture is ge- 

 nerally gradual, as is visible in the excretory ducts where the 

 membrane becomes progressively thinned and degraded, if we 

 may so express it, but in an insensible manner. If we com- 

 pare the membrane of the frontal sinuses, with that of the 

 stomach, we will certainly find great differences between 

 them, as well as between those of the tongue and of the 

 uterus; but these differences are, in a manner, connected by 



