386 



THE SKIN AND ITS APPENDAGES. 



Stratum 

 corneum. 



The following may be said concerning the vascular system of the 

 skin : The arteries which supply the skin with nutriment penetrate 

 the corium and form a characteristic network in its lowest stratum. 

 They also anastomose freely in the fascia and the subcutaneous 

 layer. From this plexus branches pass outward to form a second 

 or subpapillary plexus. From the latter, branches are again given 

 off which, without further anastomoses, pass along beneath the 

 rows of papillae and supply each separate papilla with capillary 

 twigs. These in turn pass over into venous capillaries which unite 



and form four venous 

 plexuses, one over the 

 other and in general 

 parallel to the surface 

 of the skin. The upper- 

 most venous plexus 

 lies beneath the pap- 

 illae, each venule cor- 

 responding to a single 

 row of papillae and 

 anastomosing with its 

 neighbors. The sec- 

 ond plexus is found 

 immediately beneath 

 the first, the third in 

 the lower portion of 

 the corium, and the 

 fourth at the junction 

 of the cutis and sub- 

 cutis. Near the mid- 

 dle of the subcutis the 

 arteries show a circu- 

 lar musculature, but 

 the veins are already 

 thus provided in the 



network between the cutis and subcutis, where they also seem to pos- 

 sess valves. As already stated, the subcutaneous fat is divided into 

 lobes by transverse and longitudinal bundles of connective tissue ; a 

 second system of bundles midway between the cutis and fascia 

 separates the panniculus adiposus into an upper and a lower layer. 

 The former is supplied by direct arterial branches ; the latter, by 

 branches passing backward from the cutaneous network. Those 

 regions which are subjected to great external pressure are supplied by 

 a greater number of afferent vessels the caliber of which is increased. 

 In regions where the skin is very mobile the arteries are greatly 

 convoluted. All these vascular peculiarities are present in the new- 

 born (Spalteholz). 



The lymph-vessels of the true skin are also distributed in two 

 layers a deep and wide-meshed plexus in the subcutis, and a 



Nerve-fibers 

 . in the epi- 

 dermis. 



Stratum 

 Malpighii. 



. . Papillae. 



Nerve-fiber. 



Fig. 309. Nerves of epidermis and papillae from ball of 

 cat' s foot ; X 75- 



