558 THE SKIN. 



most distinctly in the thickest portions of the skin, but may 

 be also found on the shoulders and arms, the breast, abdomen, 

 and the lower extremities, although sometimes only slightly 

 indicated. 



(3) Blood-vessels. The arteries, which supply the skin, pene- 

 trate the subjacent fasciae and anastomose with each other above 

 the fasciae ; they are more numerous in the flexor surfaces of the 

 extremities than in the extensor, and than in the trunc. The 

 largest number is found in the palmar and plantar surfaces. 

 In accordance with the accurate researches of "W. Tomsa, the skin 

 everywhere has three separate vascular districts, each of which 

 is supplied with its own arterioles and roots of veins. The 

 deepest is that of the subcutaneous fat-tissue ; the next in order 

 is that of the sweat-glands, and the most superficial belongs to 

 the derma, with its hair follicles and sebaceous glands. The 

 arterioles which supply the fat-tissue are numerous, correspond- 

 ing to the large number of capillaries ; those of the sweat-glands 

 surround the coils in a basket-like arrangement and empty into 

 two or three veinlets, one of which invariably runs upward along 

 the duct of the sweat-gland and anastomoses with veins of the 

 papillary layer. The artery, after supplying the above-named 

 formations, ascends to the papillary layer of the derma, and in 

 its course branches into capillaries which go to the hair follicles, 

 the sebaceous glands, and the papillae. Before reaching the 

 papillae, the arteriole splits into precapillary ramules, from which 

 arise the capillaries proper. These form loops which, as a rule, 

 are single, but in the largest papillae double, and unite into an 

 extended flat reticulum of a venous character. In portions of 

 the skin with large papillae there is a double layer of veins, the 

 superficial arranged in narrow and elongated meshes, the deeper, 

 on the contrary, in wide and more circular ones. These vessels 

 give rise to venous branches, uniting at acute angles into larger 

 veins, which produce arches and receive the veins of the sweat- 

 glands and the fat-lobules. The hair follicles have between the 

 two layers of the follicle wide, transversely arranged capillaries, 

 which penetrate its inner layer also. In the upper portion of the 

 follicle numerous anastomoses exist with the capillaries of the 

 papillary layer, and in this situation arise the capillary loops for 

 the supply of the sebaceous glands. All these capillaries unite 

 into an irregular venous net- work, which is lodged in the exter- 

 nal layer of the hair follicle, and anastomoses freely with the 

 venous vessels of the papillary layer. The papilla of the hair has 



