858 



THE SKIN OK INTEGUMENT. 



granules may be seen. The cells of the stratum mucosum are characterised by the 

 presence of numerous epidermic fibrils, which are coloured violet by hsernatoxylin 

 and red by carmine. These fibrils are unaffected by boiling, but swell up under 

 the action of acids and alkalies, and form the filaments of union between adjacent 

 cells. On account of their presence, L. Ranvier has named this layer the stratum 

 filamentosum. The dark colour of the negro's skin is caused by the presence of 

 numerous pigment granules in the deeper layers of the stratum mucosum ; the 

 pigment of which melanin forms an important constituent is absent from the 

 more superficial layers of the epidermis. 



3. The stratum granulosum comprises two or three layers of horizontally 

 arranged, flattened cells, scattered around the nuclei of which are elliptical or 

 spherical granules of eleidin, a substance staining deeply with carmine and haema- 

 toxylin, and probably representing an intermediate stage between the protoplasm 

 of the deeper cells and the keratin of the superficial layers. 



4. The stratum luciduin, an apparently homogeneous layer, is in reality made up 

 of several strata of flattened or irregular squames, which contain granules or 

 droplets of keratohyalin, a hyaline substance, staining less deeply than eleidin. 



5. The stratum corneum comprises several layers of flattened non-nucleated 

 squames, the more superficial of which assume the form of horny scales and are 

 from time to time removed by friction. The deeper cells contain granules of a fatty 

 material having the consistency and plasticity of beeswax, and staining with osmic 

 acid. The peripheral parts of the cells consist of keratin, a highly resistant 

 substance which is unaffected by mineral acids, and is indigestible in pepsin- 

 hydrochloric acid. 



L. Eanvier has pointed out that the stratum lucidum is really double, and has named the 

 deeper of its two layers the stratum intermedium ; this he describes as consisting of two or three 

 layers of clear cells with atrophied nuclei, while in the cell-walls the epidermic fibrils " are rolled 

 up like the threads of a cocoon." 



Eegeneration of the epidermis is generally regarded as taking place by cell proliferation in 

 the stratum germinativum, the young cells gradually passing through the polyhedral and 



granular stages, and ultimately 

 becoming the flattened squames 

 of the stratum corneum, while 

 the eleidin granules of the 

 stratum granulosum are con- 

 verted into the keratin of the 

 stratum corneum. 



Vessels and Nerves of the 

 Skin. In the subcutaneous 

 tissue the arteries form a plexus 

 from which branches extenc 

 into the corium, where the) 

 supply the hair follicles ant 

 glands, and form a seconc 

 plexus under the papilla?, t> 

 which small loops are given 

 The veins and the lymphati 

 vessels commence in th 

 papillae, and, after formin; 

 subpapillary plexuses, ope: 

 into their respective subcut 

 aneous vessels. 



The nerves of the skin var 

 in number in different parl 

 of the body ; they are extremely numerous where the sense of touch is acute, e.g. on the palms 

 surfaces of the terminal phalanges, while in the skin of the back, where the sensibility is les 

 they are fewer in number. Their different modes of ending are described on pp. 863-866. 



FIG. 735. TACTILE CORPUSCLES. 



A, End bulb (Krause). 



B, Corpuscle of Pacini "| , ,,, T, . N 



C, Corpuscle of Meissner / < after Ranvier )' 



APPENDAGES OF THE SKIN. 



The appendages of the skin are the nails, the hairs, the sebaceous glands, ao 

 the sudoriferous or sweat glands. 



Ungues. The nails (Figs. 736, 737) are epidermal structures, and represei 

 the hoofs and claws of the lower animals. The root of the nail is hidde 



