THE SKIN. 421 



part of the office of an organ of so great complexity as the 

 spleen, and containing so many other structures besides 

 blood-vessels. . The same may also be said with regard to 

 the opinion that the thyroid gland is important as a 

 diverticulum for the cerebral circulation, or the thymus 

 for the pulmonary in childhood. These, like the spleen, 

 must have peculiar and higher, though as yet ill under- 

 stood, offices. 



CHAPTEE XIV. 



THE SKLN" AND ITS SECRETION. 



To complete the consideration of the processes of organic 

 life, and especially of those which, by separating materials 

 from the blood, maintain it in the state necessary for the 

 nutrition of the body, the structure and functions of the 

 skin must be now considered : for besides the purposes 

 which it serves (i), as an external integument for the 

 protection of the deeper tissues, and (2), as a sensitive 

 organ in the exercise of touch, it is also (3), an important 

 excretory, and (4), an absorbing organ. 



Structure of the Skin. 



The skin consists, principally, of a layer of vascular 

 tissue, named the corium, derma or cutis vera, and an 

 external covering of epithelium termed the cuticle or 

 epidermis. Within and beneath the corium are imbedded 

 several organs with special functions, namely, sudoriparous 

 glands, sebaceous glands, and hair-follicles ; and on its sur- 

 face are sensitive papillce. The so-called appendages of 

 the skin the hair and nails are modifications of the 

 epidermis. 



