SKIN. ^27 



VESSELS AND NERVES OF THE SKIN. 



The arteries proceed from a network above the fascia and branch as 

 they ascend toward the surface of the skin. Their branches anastomose, 

 forming a horizontal plexus in the lower portion of the corium. From 

 this plexus branches extend to the lobules of fat and to the coils of the 

 sweat glands, about which they form "baskets" of capillaries. Other 

 branches pass to the superficial part of the corium where they again anas- 

 tomose before sending terminal arteries into the papillae. The super- 

 ficial plexus is called subpapillary, and from it the branches to the seba- 

 ceous glands and hair sheaths are derived. The papilla of a hair receives 

 an independent branch. The veins which receive the blood from the 

 superficial capillaries form a plexus immediately beneath the papillae, and 

 sometimes another just below the first and connected with it. The veins 

 from these plexuses accompany the arteries and the ducts of the sweat 

 glands to the deeper part of the corium, where they branch freely, receiv- 

 ing the veins from the fat lobules and sweat glands. Larger veins con- 

 tinue into the subcutaneous tissue where the main channels receive specific 

 names. 



The lymphatic vessels form a fine meshed plexus of narrow vessels 

 beneath the subpapillary network of blood vessels. It empties into a 

 wide meshed subcutaneous plexus. There are lymphatic vessels around 

 the hair sheaths and both sorts of glands. 



The nerves form a wide meshed plexus in the deep subcutaneous 

 tissue, and secondary plexuses as they ascend through the skin. The 

 sympathetic, non-medullated nerves supply the numerous vessels, the 

 arrector pili muscles, and the sweat glands; an epilamellar plexus out- 

 side of the basement membrane sends branches through the membrane 

 to terminate in contact with the gland cells. Medullated sensory nerves 

 end in the various corpuscles already described (page 105), and in free 

 terminations, some being intraepithelial. Medullated fibers to the hairs 

 lose their myelin and form elongated free endings with terminal enlarge- 

 ments in contact with the hyaline membrane. (The nerves to the tactile 

 hairs of some animals penetrate the hyaline membrane and terminate in 

 tactile menisci among the cells of the outer sheath.) There are no nerves 

 in the hair papilla. The corium beneath the nails is rich in medullated 

 nerves, the non-medullated endings of which enter the Golgi-Mazzoni 

 type of lamellar corpuscle (having a large core and few lamellae), or 

 they form knots which are without capsules. Elsewhere the skin contains 

 tactile corpuscles in its papillae and lamellar corpuscles in the subcutaneous 

 tissue, together with free endings in the corium and epidermis (as far 

 out as the stratum granulosum). 



