THE SKIN. 



1387 



Pigmental 

 epidermis 



Duct of 

 sweat gland 



granular layer. With the latter it constitutes the stratum intermedium. As indicated 

 by its name, the stratum lucidum appears clear and without distinct cell boundaries, 

 although suggestions of these, as well as of the nuclei of the component elements, are 

 usually distinguishable. The cells of the stratum lucidum are but little cornified and 

 differ, therefore, from those of the overlying layers ; moreover, the eleidin within the 

 cells of the stratum lucidum probably is in a fluid condition. 



The stratum corneum includes the remainder of the epidermis and consists 

 of many layers of horny epithelial cells that form the exterior of the skin. Where 

 no stratum lucidum exists, as is usually the case, the corneous layer rests upon the 

 stratum granulosum, from which its horny elements are being continually recruited. 

 During their migration towards the free surface, the cells lose their vitality and 

 become more flattened until the most superficial ones are converted into the dead 

 horny scales that are being constantly displaced by abrasion. 



The pigmentation of the skin, which even in white races is conspicuous in 

 certain regions (page 1381), depends upon the presence of colored particles chiefly 

 within the epidermis, although, when the dark hue is pronounced, a few small 

 branched pigmental connective 



tissue cells may appear within FIG. 1152. 



the subjacent corium. The dis- 

 tribution of the pigment particles 

 varies with the intensity of color, 

 in skins of lighter tints being 

 principally, and sometimes en- 

 tirely, limited to the columnar 

 cells next the corium. With 

 increasing color the pigment 

 particles invade the neighboring 

 layers of epithelium until, in the 

 dark skin of the negro, they 

 are found within the cells of the 

 stratum corneum but always 

 in diminishing numbers towards 

 the free surface. Even when 

 the cells are dark and densely 

 packed, the colored particles 



never encroach upon the nuclei, 



which therefore annear as con Section of skin ' surrounding anus, showing pigmentation of deeper 

 uu i u Ie > appeal <i=> layer of epidermis. X 50. 



spicuous pigment free areas. 



The source of the pigment within the epidermis is uncertain, by some being found 

 in an assumed transference of the colored particles from the corium, by means 

 of wandering cells or of the processes of pigmented connective tissue cells that 

 penetrate the cuticle, and by others ascribed to an independent origin in situ 

 within the epithelial elements. While it may be accepted as established that at 

 times the connective tissue cells are capable of modifying pigmentation (Karg), it 

 is equally certain that the earliest, and probably also later, intracellular pigmenta- 

 tion of the epidermis appears without the assistance of the connective tissue or 

 migratory cells. 



The blood-vessels of the skin are confined to the connective tissue portion 

 and never enter the cuticle. The arteries are derived either from the trunks of the 

 subjacent layer as special cutaneous branches destined for the integument, or indi- 

 rectly from muscular vessels. When the blood supply is generous, as in the palms 

 and soles and other regions subjected to unusual pressure or exposure, the arteries 

 ascend through the subdermal layer to the deeper surface of the corium where, 

 having subdivided, they anastomose to form the siibcutaneous plexus (rete arteriosura 

 cutaneum). From the latter some twigs sink into the subdermal layer and contribute 

 the capillary net-works that supply the adipose tissue and the sebaceous glands. 



Other twigs, more or less nunierous, pass outward through the deeper part of 

 the corium and within the more superficial stratum unite into a second, subpapillary 

 plexus (rete arteriosum subpapillare), that extends parallel to the free surface and 



