CHAPTER XL 



THE SKIN AND ITS APPENDAGES 



THE skin is composed of two parts, epidermis or cuticle, and dermis 

 or cutis vera. 



The Epidermis is a thick stratified epithelium. The deeper 

 layers are composed of protoplasmic cells, and form the rete mucosum, 

 or Malpighian layer; the surface layers are hard and horny; this 

 horny layer is the thickest part of the epidermis, and is specially 

 thick on the palms and soles, where it is subjected to most friction. 

 It is in the cells of the Malpighian layer that pigment granules are 

 deposited in the coloured races. 



Between the horny layer and the Malpighian layer are two 

 intermediate strata, in which the transformation of protoplasm into 

 horny material (keratin) is taking place. In the first of these that 

 is, the one next to the Malpighian layer the cells are flattened, 

 and filled with large granules of eleidin, an intermediate substance 

 in the formation of horn. This layer is called the stratum 

 granulosum. 



Above this are several layers of clear, more rounded cells, which 

 constitute the stratum lucidum; and above this the horny layer 

 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 

 cells; the newly-formed cells push towards the surface those pre- 

 viously formed, in their progress undergoing the transformation 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 papilla ; the epidermis is moulded over these, 



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