THE DBKMIS OR COEIUM 355 



Examination of the epidermis on the hand shows it to 

 be raised in ridges parallel to one another, and so arranged 

 as to form various patterns. Since these patterns do not 

 change throughout life they serve to identify criminals. 

 A hand lens also shows that the epidermis is perforated 

 at frequent intervals. These perforations, or pores, are the 

 openings of tiny ducts which extend downward to the 

 sweat glands of the dermis and discharge the perspiration. 

 In other places the epidermis is pierced by hairs which 

 also have their source in the dermis. 



As has been already noted, no blood vessels enter the 

 epidermis; the active cells receiving their food from the 

 Ijmiph of the dermis. Nerve fibers are wanting in the upper 

 layers of the epidermis, but fibers do extend into the lower 

 cells, so that when this layer is separated from the dermis, 

 as in a blister, the prick of the needle can still be felt by the 

 epidermal covering of the blister though it produces no 

 sensation of pain. 



The dermis or cerium. — The dermis or true skin is com- 

 posed mainly of a network of connective tissue rich in 

 elastic and white fibers. In tanning operations it is this 

 laj'-er that is transformed into leather. The dermis is 

 loosely coimected to underlying parts by a layer of fibers 

 called the subcutaneous layer, and this loose connection 

 permits the skin to move freely over the underlying flesh. 

 Sometimes this subcutaneous layer is the seat of fat 

 deposits, especially in the layers that cover the abdomen. 

 These fat layers tend to protect the body from cold. The 

 surface of the dermis that is in contact with the epidermis 

 is raised in a great many tiny projections called papilla). 

 These papillae are arranged in rows and are the cause of 

 the ridged appearance of the epidermis. Some contain a 



