ANATOMY OF THE SKIN. 113 



Layers of the Skin. The skin is naturally divided into 

 two principal layers, which may be readily separated from 

 each other by maceration. These are, the true skin (cutis 

 vera, derma, or corium), and the epidermis, cuticle, or scarf- 

 skin. The true skin is attached to the subjacent structures, 

 more or less closely, by a fibrous structure called the sub- 

 cutaneous areolar tissue, in the meshes of which we com- 

 monly find a certain quantity of fatty tissue. This layer 

 is sometimes described under the name of the panniculus- 

 adiposus. The thickness of the adipose layer varies very 

 much in different parts of the general surface and in differ- 

 ent persons. There is no fat beneath the skin of the eyelids, 

 the upper and outer part of the ear, the penis, and the scro- 

 tum. Beneath the skin of the cranium, the nose, the neck, 

 and the dorsum of the hand and foot, the knee and the elbow, 

 the fatty layer is about -% of an inch in thickness. In other 

 parts it usually measures from ^ to ^ of an inch. 1 In very 

 fat persons it may measure one inch or more. Upon the 

 head and the neck, in the human subject, are muscles at- 

 tached more or less closely to the skin. These are capable 

 of moving the skin to a slight extent. Muscles of this kind 

 are largely developed and quite extensively distributed in 

 some of the lower animals. 



There is no sharply-defined line of demarcation between 

 the cutis and the subcutaneous areolar tissue ; and the under 

 surface of the skin is always irregular, from the presence of 

 numerous fibres which are necessarily divided in detaching 

 it from the subjacent structures. The fibres which enter into 

 the composition of the skin near its under surface become 

 looser in their arrangement, the change taking place rather 

 abruptly, until they present large alveolae, which generally 

 contain a certain amount of adipose tissue. 



The layer called the true skin is subdivided into a deep, 

 reticulated, or fibrous layer, and a superficial portion, called 



1 KRAUSE, in WAGNER'S Handucdrterbuch der Physiologic, Braunschweig, 1844, 

 Bd. ii., S. 116. 



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