438 



STRUCTURE OF THE EPIDERMIS. 



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Stratum 

 Malpighii. 



corneum consist of several layers of dry horny non-nucleated squames, which swell up in solu- 

 tion of caustic soda (fig. 294, E). [It is always thickest where intermittent pressure is applied, 

 as on the sole of the foot and palm of the hand.] The next layer is the stratum lucidum, which 

 is clear and transparent in a section of skin, hence the name, and consists of compact layers of 

 clear cells with vestiges of nuclei. Under this is the rete mucosum or rete Malpighii (fig. 294, d), 

 consisting of many layers of nucleated protoplasmic epithelial cells which contain pigment in 

 the dark races, and in the skin of the scrotum, and around the anus. [The superficial cells are 

 more fusiform and contain granules which stain deeply with carmine. They constitute, 3, 

 the stratum granulosum. In these cells the formation of keratin is about to begin, and the 

 granules have been called eleidin granules by Ranvier. They are chemically on the way to 

 he transformed into keratin. All corneous structures contain similar granules in the area where 



the cells are becoming corneous. Then follow 

 several layers of more or less polyhedral cells, 

 softer and more plastic in their nature, and ex- 

 hibiting the characters of so-called "prickle 

 cells" (fig. 294, R). [The spaces between the 

 fibrils connecting adjacent cells are lymph spaces.] 

 The deepest layers of cells are more or less 

 columnar, and the cells are placed vertically upon 

 the papilla?. Granular leucocytes or wandering 

 cells are sometimes found between these cells. 

 This, the fourth layer, has been called the stratum 

 Malpighii. The rete Malpighii dips down between 

 adjacent papilla? and forms interpapillary pro- 

 cesses. According to Klein, a delicate basement 

 membrane separates the epidermis from the true 

 skin. ] The superficial layers of the epidermis are 

 continually being thrown off, while new cells are 

 continually being formed in the deeper layers of 

 the skin by proliferation of the cells of the rete 

 Malpighii. There is a gradual change in the 

 microscopic and chemical characters of the cells 

 from the deepest to the superficial layers of the 

 epidermis. [In a vertical section of the skin 

 stained with picro-carmine, the S. granulosum 

 is deeply stained red, and is thus readily distin- 

 guished amongst the other layers of the epidermis.] 

 [Epider- ( (1) Stratum corneum, \ ut j c j e 

 mis 1 (2) Stratum lucidum, \ 

 (fig. 1 (3) Stratum granulosum, ) Rete 

 293), ( (4) Stratum Malpighii, \ Mucosum.] 



No pigment is formed within the epidermis 

 itself; when it is present, it is carried by leucocytes 

 from the subcutaneous tissue {Richl, Ehrmann, 

 Achy). This explains how it is that a piece of 

 white skin, transplanted to a negro, becomes 

 black (Karg). 



The chorium (fig. 294, I, C) is beset over its 

 entire surface by numerous (0*5 to O'l mm. high) 

 papillae (fig. 294), the largest being upon the volar surface of the hand and foot, on the nipple 

 and glans penis. Most of the papillae contain a looped capillary (</), while in certain regions 

 some of them contain a touch-corpuscle (fig. 295, a). The papilla? are disposed in groups, 

 whose arrangement varies in different parts of the body. In the palm of the hand and sole of 

 the foot they occur in rows, which are marked out by the existence of delicate furrows on the 

 surface visible to the naked eye. The chorium consists of a dense network of bundles of white 

 fibrous tissue mixed with a network of elastic fibres, which are more delicate in the papilla?. In 

 silversmiths the elastic fibres are blackened by the partial deposition of reduced silver, and the 

 same obtains in those who take silver nitrate in such quantity as to produce argyria. The con- 

 nective-tissue contains many connective-tissue corpuscles and numerous leucocytes. The deeper 

 connective-tissue layers of the chorium gradually pass into the subcutaneous tissue, where they 

 form a trabecular arrangement of bundles, leaving between them elongated rhomboidal spaces 

 filled for the most part with groups of fat cells (fig. 294, a, a). [In microscopic sections, after 

 the action of alcohol, the fat cells not unfrequently contain crystals of margarin.] The long axis 

 of the rhomb corresponds to the greater tension of the skin at that part (C. Langcr). In some 

 situations the subcutaneous tissue is devoid of fat [penis, eyelids]. In many situations, the 

 skin is fixed by solid fibrous bands to subjacent structures, as fascia?, ligaments or bones 





Fig. 293. 

 Vertical section of the human epidermis ; 

 the nerve-fibrils, n, b, stained with 

 gold chloride. 



