THE STRUCTURE AND FUNCTIONS OF THE SKIN. 



343 



curved lines, separated from each other by depressions. Thus they may 

 be easily seen on the palm, whereon each raised line is composed of a 

 double row of papillae, and is intersected by short transverse lines or fur- 

 rows corresponding with the interspaces between the successive pairs of 

 papillae. Over other parts of the skin they are more or less thinly scat- 

 tered, and are scarcely elevated above the surface. Their average length 



FIG. 234. Vertical section of skin. A. Sebaceous gland opening into hair follicle. B. Muscular 

 fibres. C. Sudoriferous or sweat-pland. D. Subcutaneous fat. E. Fundus of hair-follicle, with 

 hair-papillae. (Klein and Noble Smith.) 



is about -j-J-jj- of an inch, and at their base they measure about ^-g- of an 

 inch in diameter. Each papilla is abundantly supplied with blood, re- 

 ceiving from the vascular plexus in the cutis one or more minute arterial 

 twigs, which divide into capillary loops in its substance, and then re- 

 unite into a minute vein, which passes out at its base. This abundant 

 supply of blood explains the turgescence or kind of erection, which they 

 undergo when the circulation through the skin is active. The majority, 



