410 



STRUCTURE OF THE SKIM. 



-P& 



BP 



THE SKIN. 



The skin consists of the cutis vera or corium, and the cuticle or epidermis. 



The epidermis, cuticle, or scarf-skin, belongs to the class of stratified 

 epithelia, the general nature of which has been already considered. It forms a pro- 

 tective covering over every part of the true skin. The thickness of the cuticle varies 

 in different parts of the surface, measuring in some places not more than s^th, and 



Fig. 466. SECTION OF HUMAN EPIDER- 

 MIS WITH TWO VASCULAR PAPILLA 



oy THE CORIUM. (Heitzmann.) 



B.P, loop of capillary vessels in 

 papilla ; V", rete mucosum ; P.L, 

 stratum granulosum ; E, stratum cor- 

 neum ; D to p, duct of sweat-gland 

 passing through the epidermis. 



in other parts, as much as J T th 

 of an inch (about a millimeter), 

 or even more than this in some 

 individuals. It is thickest in 

 the palms of the hands and 

 soles of the feet, where the skin 

 is much exposed to intermittent 

 pressure, and it is not impro- 

 bable that such pressure may 

 serve to stimulate the adjacent 



true skin to a more active formation of epidermis ; but the difference does not 

 depend immediately on external causes, for it is well marked even in the foetus. 



The 'more firm and transparent superficial part, or horny layer, of the epi- 

 dermis, may be separated after maceration from the deeper, softer, more opaque, 

 and recently formed part, which constitutes what is called the Malpighian layer, or 

 rete mucosum. 



The under or attached surface of the cuticle is moulded on the adjoining surface 

 of the corium, and, when separated by maceration or putrefaction, presents impres- 

 sions corresponding exactly with the papillary or other eminences, and the furrows 

 or depressions of the true skin ; the more prominent inequalities of the latter are 

 marked also on the outer surface of the cuticle, but less accurately. Fine tubular 

 prolongations of the cuticle sink down into the ducts of the sweat-glands, and are 

 often partially drawn out from their recesses when the cuticle is detached, appearing 

 then like threads proceeding from its under surface. 



Structure. The cuticle is made up of cells agglutinated together in many 

 irregular layers. The deepest cells are elongated in figure, and placed perpendi- 

 cularly on the surface of the corium (fig. 467, e) ; they are denticulate at their 

 lower ends, and fit into corresponding fine denticulations of the corium. The 

 perpendicular cells generally form one stratum ; above them are cells of a more 

 rounded or polyhedral shape (d). The cells have fine intercellular clefts or chan- 

 nels between them, bridged across by fibres which pass from cell to cell, as in all 

 stratified epithelia (see p. 196). These so-called " spiny cells" form several strata; 

 above, they become gradually more flattened, conformably to the surface, until a 

 layer, often incomplete, is reached in which the cells have a markedly granular appear- 

 ance (Langerhans). This has been termed the stratum granulosum. The granules 

 in the cells are composed of a peculiar matter (eleidin of Ranvier, Iceratohijalin of 



