152 THE SKIN. 



,. . -, f Stratum corneum. 



Horny portion of epidermis j Stn!t/um lucidum . 



( Stratum granulosum. 

 Retemaconim | Stratum Malpighii. 



Of these layers the strata corneum and Malpighii are the 

 thickest, most prominent, and always present; the strata 

 lucidum and granulosum are much thinner, less conspicuous, 

 and where the epidermis is thin may be quite indistinguish- 

 able. There are no bloodvessels or capillaries in the epider- 

 mis, but lymph is probably able to percolate between the cells. 



The stratum Malpig-hii (or stratum germinativum) consists 

 of about ten to twenty-five layers of .deeply staining sphe- 

 roidal epithelium-cells resting on the corium. Into this 

 stratum project the papillae which stud the surface of the 

 corium, the intervals between the papillse being filled with 

 epithelial cells. The lowermost cells of the Malpighian 

 stratum form a single layer of tall columnar cells arranged 

 perpendicular to the surface of the papilla and corium ; this 

 layer forms a quite distinct stratum. The other cells of the 

 Malpighian layer, larger than the columnar cells, are spheroi- 

 dal in shape, or polyhedral from mutual pressure, becoming 

 somewhat flattened above. They are disposed irregularly, not 

 in uniform layers, and have characteristic " vesiculated nuclei " ; 

 that is, their nuclei are surrounded by or seem to lie in a clear 

 vesicular space. The surfaces of these cells are closely beset 

 with ridges, or " intercellular bridges," causing the cells to 

 appear in cross-section as if studded with projecting prickles 

 or spines, whence they are often called prickle- cells. The 

 ridges of adjacent cells unite edge to edge, and the minute 

 communicating channels left between them probably enable 

 lymph to pass between these cells for the nourishment of the 

 non-vascular epidermis. The cells of the deeper portion of 

 the stratum Malpighii contain pigment, which gives color to 

 the skin, especially in freckles and dark-skinned races. The 

 Malpighian layer contains terminal nerve-fibrils and tactile 

 cells. 



The stratum granulosum rests upon the stratum Malpighii, 

 the two merging together without sharp dividing-lines. It is 

 not always very distinct, but in thick epidermis it appears 



