THE CUTANEOUS TISSUE. 123 



tractility, elasticity, and extensibility, which are no doubt 

 employed in their function of circulating the lymph, but 

 this point is by no means yet satisfactorily settled. 



CHAPTER VI. 



T.HE CUTANEOUS TISSUE. 



ANALYSIS. 

 IMPORTANCE, EXTENT, FORM, STRUCTURE, FUNCTIONS AND RELATION!. 



THIS tissue, especially its external portion, has received 

 the names of dermoid, tegumentary, compound villous, or 

 follicular membranes. Its importance may be estimated 

 from its early development, vast extent, complexity of 

 structure, variety of function, diversity of relations, and 

 number of diseases. 



In the language of M. Beclard, this tissue is the " most 

 universally extended in the animal kingdom; it is the first 

 which is distinct and figured in the embryo; it is on it 

 and by it the rest of the body is formed; and it con- 

 tains the most essential functions, is often changed by 

 disease, is the part on which all foreign substances produce 

 impressions, and most therapeutic agents are applied." 



The extent of this element is commensurate with the 

 whole external and internal surface of the body, wherever 

 exposed to the contact of foreign substances. Its form has 

 been compared to two canals, the one wide and external, 

 the other narrow and internal, and the two continuous, 

 the intervening space being occupied by the rest of the body. 

 From this peculiarity of form, it consists of two great 

 divisions. 



1st. The skin and its appendages, forming the outer canal 

 or external surface. 



2d. The mucous membrane, forming the inner canal or 

 internal surface. 



