356 EXCEBTION 



knot of capillaries which are supplied with blood from 

 a small artery and empty into small veins. They enable 



Fig. 163 — Dermal papilla;; the black lines represent capillaries, and the wliite 

 lines, nerves. The nerves end in bundles called corpuscles. 



the blood to be brought near the active, epidermal cells. 

 The other papillae contain dehcate sense organs connected 

 by nerves with the central nervous system. The func- 

 tion of this latter kind will be discussed more fully in our 

 study of the nervous system. Some are sensitiA'^e to touch, 

 and some to cold, and to them is due the power of skin to 

 respond to external sensory stimuli. They are especially 

 abundant at the ends of the fingers, thereby giving to these 

 members their delicate perception of touch. We may dis- 

 tinguish these two kinds of papillae by calling one kind 

 blood papillae and the other nerve papillae. Evidently the 

 dermis is well provided with blood vessels and nerves. 

 Except for these papillae, the dermis is usually smooth, but 

 in old age the absorption of fat from the subcutaneous 

 layer permits the skin to shrink and form wrinkles. 



Besides these papillae the dermis shows other structures, 

 sweat and sebaceoiis glands, while hairs and nails are sim- 



