442 



EXCRETION 



The so-called appendages of the skin the hair and nails are modifications 

 of the epidermis. 



The epidermis is composed of several strata of cells of various shapes and 

 sizes; it closely resembles in its structure the epithelium of the mucous mem- 

 brane that lines the mouth or covers the cornea. The following four layers 

 may be distinguished. 



FIG. 305. Vertical Section of Skin. A, Sebaceous gland opening into hair follicle; 

 B, muscular fibers; C, sudoriferous or sweat gland; D, subcutaneous fat; E, fundus of hair 

 follicle, with hair-papillae. (Klein.) 



The stratum lucidum, a homogeneous membrane, consisting of squamous 

 cells closely arranged, in some of which a nucleus can be seen. Stratum 

 granulosum, consisting of one layer of flattened, fusiform, distinctly nucleated 

 cells. Stratum Malpighii or rete mucosum consists of many strata of cells. 

 The deepest cells, placed immediately above the cutis vera, are columnar 

 with oval nuclei, succeeded by a number of layers of more or less polyhedral 

 cells with spherical nuclei; the more superficial layers are considerably 

 flattened. The deeper surface of the rete mucosum is accurately adapted 



