106 



NORMAL HISTOLOGY. 



CHAPTEK XIV. 



THE SKIN. 



The epidermis of the skin is derived from the epiderm of the 

 embryo, while the corium is largely of mesodermic origin. Its chief 

 functions are protection, respiration, and excretion. 



OUTLINE OF SKIN. 



Derivation. 



Structure 



Epidermis 



Stratum corneum. 

 Stratum lucidum. 

 Stratum granulosum. 

 Stratum malpighii. . . . 



Pigment granules. 

 Prickle cells. 



Appendages 



Coriuni 



Glands 



Nails 



f Fibrous connective tissue. 

 . . . . ) Elastic fibres. 



L Blood vessels, nerves, etc. 



Nail bed. 

 Matrix. 



Cuticle. 

 Shaft <! Cortex. 



Medulla. 



{ Bulb. 



Root <| Papilla. 



I Follicle. 



Structure, The skin consists of two layers the epidermis, or 

 cuticle, and corium, or cutis. The epidermis is constituted of strati- 

 fied squamous epithelium disposed in four layers. These are the 

 stratum corneum, stratum lucidum, stratum granulosum, and 

 stratum Malpighii. The stratum corneum is superficial and is com- 

 posed of flattened corneous cells which have lost their protoplasm 

 and, by desquamation, are continually cast off. The stratum luci- 

 dum, occurs next, and comprises a narrow zone in which the cells 

 exhibit an approach to the flattened scales of the outer stratum. 



