't 



124 SKIN AND ITS APPENDAGES. 



Though these two divisions present striking differences 

 at first sight, yet they are so closely allied in structure, 

 being regarded as essentially the same, that we shall ex- 

 amine both as belonging to the same tissue. 



The skin can be traced as gradually sliding into, and 

 becoming insensibly lost in the mucous membrane at all 

 the natural apertures, as the mouth, anus, prepuce, labia, 

 &c., showing the continuity of the two divisions ; and their 

 identity is further established by their being convertible the 

 one into the other. For instance, in the axillee, nates and 

 other parts, where opposing surfaces of the skin come in 

 contact and are not kept clean, the skin will become moist 

 and soft, and present all the appearances of mucous mem- 

 brane. On the other hand, mucous membrane, as in pro- 

 lapsus of the rectum and vagina, by being exposed becomes 

 dry, and assumes all the peculiar characters of skin. 



SKIN AND ITS APPENDAGES. 



The skin, (cutis, fopjta,) as already remarked, covers the 

 whole external surface of the body, and according to the 

 prize essay of Mr. Wheelock, measures in extent 2,500 inches. 

 Its color varies from white to black, having all the inter- 

 mediate shades depending on the different races of man- 

 kind, and the difference in climate, age and exposure. Its 

 density also varies, being thicker in the black than the 

 white, and much more dense in some parts of the body 

 than others, as in the palm of the hand and sole of the 

 foot. It has two surfaces, the one free and exposed to 

 external bodies, the other adherent to parts beneath by cel- 

 lular tissue, and in the scalp and neck, closely connected with 

 muscular structure, as over the occipito-frontalis and pla- 

 tyma myoides. The free surface presents a variety of ob- 

 jects of study, as inequalities of elevation and depression, 

 folds and wrinkles, openings or pores, and various grades of 

 softness and moisture, all of which will be more particular- 

 ly noticed in the account of its structure. The adhering sur- 

 face, by its loose cellular tissue, generally admits of free 

 motion between the skin and adjacent parts. 



