THE SKIN 



107 



cells of the deeper layers. The newly formed cells, as they grow, push 

 towards the surface those which were previously formed, and in their 

 progress the latter undergo a chemical transformation, which converts 

 their protoplasm into horny material. This change seems to occur 

 at the stratum granulosum (see fig. 130) ; the granules which occupy 

 the cells of that layer being composed of a substance termed ejeidin, 

 which is transformed into keratin. 



No blood-vessels pass into the epidermis, but it receives nerves 

 which ramify between the cells of the rete mucosum in the form of 

 fine varicose fibrils (fig. 129). 



FlG. 130. PORTION OF KI'IDEUMIS FROM A SECTION OF THE SKIN OF THE 

 FINGER, COLOURED WITH PICROCARMINATK OF AMMONIA. (Raiwier.) 



a, stratum corneum ; 6, stratum lucidum with diffused flakes of eleidin ; c, stratum granu- 

 losum, the cells filled with drops of eleidin ; d, prickle-cells ; e, dentate projections by 

 which the deepest cells of the epidermis are fixed to the cutis vera. 



The cutis vera or corium is composed of dense connective tissue, 

 which becomes more open and reticular in its texture in its deeper 

 part, where it merges into the subcutaneous tissue. The superficial or 

 vascular layer of the corium bears minute papilla, which project up 

 into the epidermis, which is moulded over them. These papillae for 

 the most part contain looped capillary vessels (fig. 137), but some, 

 especially those of the palmar surtace oil the liaiid and fingers, and the 

 corresponding part of the foot, contain tactile corpuscles, to which 

 medullated nerve -fibres pass (fig. 97, b). 



In some parts of the body (scrotum, penis, nipple, and areola), 

 involuntary muscular tissue occurs in the deeper portions of the cutis 

 vera, and in addition, wherever hairs occur, small bundles of this 

 tissue are attached to the hair-follicles. 



The blood-vessels of the skin are distributed almost entirely to the 

 surface, where they form a close capillary network, sending up loops 



