336 MOEBID ANATOMY OF THE SKIN. 



furnisKed with its own afferent and efterent caj^illaiy vessel : tlie 

 two communicate either directly, by a simple loop, or — more 

 commonly — by a number of loops. These vessels are all remark- 

 ably tortuous ; it sometimes happens that the afferent and effererit 

 trunks of a simple capillary loop are twisted round each other 

 corkscrew-fashion till they unite at the apex of the papilla. The 

 point at which they unite — the summit of the curve — is always 

 much dilated. Everything points to the conclusion that in the 

 cutaneous papilla the lateral pressure of the blood must be 

 augmented and the current of the circulation retarded. Indeed 

 we may look upon the vascular apparatus of the larger papillse, 

 which are provided with several communicating loops, in the 

 light of small retia mirabilia.* They stand towards the vascular 

 network of the cutis in the relation of diverticula ; like the side- 

 channels of a stream, in which the current experiences greater 

 resistance, notwithstanding that the fall is the same in either 

 case. This arrangement may have a physiological importance of 

 its own, it may be of the utmost moment for the respiratory 

 function of the skin ; apart from this however, it serves to 

 explain how it is that hyperasmic conditions of the skin, to what- 

 ever cause they may be due, are peculiarly intense and lasting, 

 and lead to more serious consequences in the papillary body than 

 elsewhere. 



What is true of the papillary body as a whole is peculiarly 

 true of the smaller, but all the more thickly-set papilla which 

 surround the orifices of the hair-follicles (fig. 109). Here too 

 therefore, in connexion with hypersemic conditions of the entire 

 tegumentary system, the dilatation of the capillaries, the slowing 

 of the blood-current, and all the derived phenomena, attain their 

 maximum intensity. In a word, the vascular apparatus of the 

 subepithelial connective tissue of the skin is disposed in such a 

 way as to bring the limitation of so large a number of derma- 



* In injected specimens of the kidney, I have often observed that 

 the Malpighian glomeruli are also made up of two or three capillary 

 tufts (Gefassbaumchen), each of which corresponds precisely to the 

 capillary tuft of a papilla. It is not impossible that the Malpighian 

 glomeruli may originate as papillary excrescences from the coecal ends 

 of the uriniferous tubes. (?) {Cf. Eenle, Handbuch d. Systemat. 

 Anatomie, Braunschweig, 1862. Eingeweidelehre, p. 310, a, h, figs. 

 237. 238.) 



