576 



THE SKIN AND ITS APPENDAGES 



[CH. XXXVIII. 



proper, many strata deep, begins. The cells become more and more 

 scaly as they approach the surface, where they lose their nuclei and 

 eventually become detached. 



The epidermis grows by a multiplication of the deepest layer of 



FIG. 438. Surface of a white hair, magnified 160 diameters. The wavy lines mark the upper or free 



edges of the cortical scales. B, separated scales, magnified 350 diameters. (Kolliker.) 



cells (fig. 436 e); the newly-formed cells push towards the surface 

 those previously formed, in their progress undergoing the transfor- 

 mation into keratin. 



The epidermis has no blood-vessels; nerve-fibrils pass into its 



deepest layers, and ramify between the 

 cells. 



The Dermis is composed of dense 

 fibrous tissue, which becomes looser and 

 more reticular in its deeper part, where 

 it passes by insensible degrees into the 

 areolar and adipose tissue of the sub- 

 cutaneous region. The denser superficial 

 layer is very vascular, and is covered 

 with minute papillce ; the epidermis is 

 moulded over these, and in the palms 

 and soles, where the papillae are largest 

 and are disposed in rows, their presence 

 is indicated by the well-known ridges 

 on the surface. 



The papillae contain loops of capil- 

 FIG. 430. -Longitudinal section of a laries, and in some cases, especially in 



hair follicle, a and 6, external root- ,- -, *> .1 i i j n It. 



sheath; c, internal root-sheath; the palm of the hand and fingers, they 

 SfiyTteS^y/aS: contain tactile corpuscles (which will be 

 vessels of the hair papiiia ; h, more f ully described in connection with 



dermic coat. (Cadiat.) J ~ .,, 



the sense of touch). Special capillary 



networks are distributed to the sweat-glands, sebaceous glands, and 

 hair follicles. 



The deeper portions of the dermis in the scrotum, penis, and 

 nipple, contain involuntary muscular tissue; there is also a bundle of 

 muscular tissue attached to each hair follicle. 



