THE SKIN. 209 



the hair, is not of uniform character throughout, and lias been divided 

 into a number of layers, to which different observers have given 

 special names. The group of cells surrounding the papilla are the 

 seat of the multiplication which results in the growth of the hair. 

 Upon the surface of the shaft these cells become transformed into 

 thin scales, each of which overlaps that above it. This very thin 

 layer is called the "cuticle" of the hair. Beneath the cuticle the 

 cells are crowded together into fusiform or fibrous elements, which 

 make up the chief mass of the hair-shaft. In the centre of this 

 mass there is sometimes a line of more loosely aggregated cells, 

 forming the " medulla " of the hair. When this is present the sur- 

 rounding part of the shaft, between it and the cuticle, is known as 

 the "cortex" (Figs. 185 and 186). 



The sebaceous glands (Fig. 181, d) are sacculations in the corium 

 near the hair- follicles, which are tilled with epithelial cells. The 

 cells at the periphery divide, and, as they increase in size, push 



Fig. 186. 



Hair-follicle from the human scalp. (Mertsching.) Cross-section from middle third of 

 the follicle: 6, longitudinal and encircling layers of the fibrous coat; c, hyaline layer, 

 formed of an outer faintly fibrillated and an inner more homogeneous lamina, & ; e, outer 

 root-sheath, continuous with rcte mucosum of epidermis ;/, Henle's sheath; <?, Huxley's 

 layer ; h, cuticle of root-sheath ; fc, cuticle of hair ; I, cortical cells of the hair ; m, 

 medulla. 



each other toward the centres of the sacs. Here they undergo a 

 fatty degeneration, ending in destruction of the cells and the forma- 

 tion of an oily secretion, the sebum, which is discharged into the 

 hair-follicle a short distance below its opening on the surface of the 

 skin. The sebum is a lubricant for both the hair and the epi- 

 dermis (Fig. 187). 



The color of the epidermis and of the hair is due to a pigmenta- 



14 





