THE SKIN. 



321 



IMS 



The blood-vessels of the skin are confined to the connective tissue 

 portion and never enter the cuticle. The arteries are derived either from the 

 trunks of the subjacent layer as special cutaneous branches destined for the 

 integument, or indirectly from muscular vessels. When the blood-supply is 

 generous, as in the palms and soles and other regions subjected to unusual 

 pressure or exposure, the arteries ascend through the subdermal layer to the 

 deeper surface of the corium where, having subdivided, they anastomose to 

 form the subcutaneous plexus. 

 From the latter some twigs sink 

 into the subdermal layer and con- 

 tribute the capillary networks that 

 supply the adipose tissue and the 

 sebaceous glands. Other twigs, 

 more or less numerous, pass out- 

 wards through the deeper part of 

 the corium and within the more 

 superficial stratum unite into a 

 second, subpapillary plexus, that 

 extends parallel to the free surface 

 and beneath the bases of the pa- 

 pillae. The latter are supplied by 

 the terminal twigs which ascend 

 vertically from the subpapillary 

 network and break up into capil- 

 lary loops that occupy the papillae 

 and lie close beneath the epidermis 

 (Fig. 366). The arrangement of 

 the cutaneous veins, more complex 

 than that of the arteries, includes 

 four plexuses lying at different 

 levels within the corium and ex- 

 tending parallel to the surfaces. 

 The first and most superficial one 

 is formed by the union of the radi- 

 cles returning the blood from the 

 papillae.. The component veins lie 

 below and parallel to the rows of 

 papillae and immediately beneath 

 the bases of the latter. At a 

 slightly lower level, in the deeper 



part of the Stratum papillare, the FIG. 366. Section of injected skin, showing general 

 i_ 1 j. < arrangement of the blood-vessels: the terminal loops 



venous channels proceeding from occupy the papillae, x 30. 

 the subpapillary network join to 



form a second plexus. A third occurs about the middle of the corium, 

 while the fourth shares the position of the subcutaneous arterial plexus at 

 the junction of the corium and subdermal strata. The deepest plexus receives 

 many of the radicles returning the blood from the fat and the sweat-glands, 

 the remainder being tributary to the veins accompanying the larger arteries 

 as they traverse the tela subcutanea. 



The lymphatics of the skin are well represented by a close superficial 

 plexus within the papillary stratum of the corium into which the terminal 

 lymph-radicles of the papillae empty. The relation of these channels to the 

 interfascicular connective tissue spaces is one only of indirect communication, 



