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NORMAL HISTOLOGY. 



BLOOD-VESSELS, LYMPHATICS, AND NERVES OF THE SKIN. 



The blood-vessels supplying the skin are arranged as three sets, 

 which occupy different levels, and are destined especially for the 

 structures lying within the respective layers. The larger arterial 

 vessels run between the superficial fasciae and the integument, 

 generally parallel to the latter, while perpendicular branches are given 

 off which pass towards the free surface and early in their course 

 provide twigs for the supply of the deep-lying fat- clusters, among 

 which the arterioles break up into the capillary net-works. At a 

 somewhat higher level branches are given off to the sweat-glands, 

 superficially to which a net-work is formed by the terminal branches 

 of the ascending arteries, and constitutes a rich subepithelial 

 reticulum distributed to the outermost stratum of the corium. 

 Where well developed, the papillae receive vascular tufts and loops 

 from the subepithelial net-work, the disposition of the loops corre- 

 sponding with the simple or compound character of the papillae. 

 Numerous twigs also provide for the nutrition of the hair-follicles, 

 around which the longitudinal arterioles are connected by the trans- 

 versely-disposed capillary net-works encircling the follicles ; loops are 

 given off to supply the hair-papillae, as well as small branches to the 

 sebaceous glands and the hair-muscles. The veins follow the gen- 

 eral arrangement of the arterial branches. The follicles of the 

 conspicuous tactile hairs of the lower animals are surrounded by 

 the large venous spaces which occupy the cavernous tissue situated 

 between the longitudinal and the circular coat of the fibrous sheath. 



The numerous lymphatics of the skin are arranged in two gen- 

 eral sets, those extending within the corium and forming the 

 superficial reticulum, and those situated within the subcutaneous 

 tissue and following the larger blood-vessels. The superficial 

 lymphatics begin as the interfascicular clefts of the corium, some of 

 which are contained within the papillae ; these irregular spaces, with 

 their imperfect lining of connective-tissue plates, communicate with the 

 more definite lymph-vessels, which anastomose to form the plexus 

 extending throughout the corium slightly beneath the plane of the 

 closer-meshed reticulum of blood-capillaries. Special net- works of 

 lymph-capillaries surround the hair-follicles and the glands. The 

 deeper set of lymphatics lie within the subcutaneous tissue and con- 

 stitute a loose reticulum of larger vessels, which freely communicate 

 with the closer superficial lymphatic net-works as well as with those sur- 

 rounding the adjacent hair-follicles and the glands. Each of the larger 

 blood-vessels is usually accompanied by two lymphatic trunks of 

 considerable size, which, by means of numerous transverse branches, 

 freely communicate and enclose the blood-vessels within their meshes. 



