CH. XXV] 



STRUCTURE OF HAIRS 



637 



seen like a mosaic on the surface of the hair, the outermost ones 

 overlapping each other like slates on a roof with the same function 

 of letting the water run off. 



We saw that a feather originated as a little knob, the outside 

 of which was composed of horny cells, while the interior consisted 

 of soft living tissue supplied with blood-vessels ; a hair on the other 

 hand makes its appearance as a cylinder of horny cells growing down 

 from the epidermis into tine dermis underneath. This cylinder then 

 becomes split into an outer sheath and an inner core, the latter of 

 which elongates and forms the hair, while the former remains 



FIG. 314. Section through the skin of a Mammal. Highly magnified. 

 Diagrammatic. 



1. Outer layer of dead horny cells which are rubbed off from time to time, 

 Stratum corneum. 2. Deeper layer of cells retaining their protoplasm, 



Stratum Malpighii. 1 and 2 form the epidermis and are ectodermal in 



origin. 3. Dermis or Corium. 4. A hair. 5. Sweat-gland. 



6. Opening of the duct of the sweat-gland. 7. Sebaceous or fat gland. 

 8. Erector muscle of the hair. 9. Connective tissue fibres of the dermis. 

 10. Blood-vessel. 11. Vascular papilla at base of the hair follicle. 



stationary and constitutes the follicle of the hair. The growth of 

 the hair is rendered possible by a little plug of dermis carrying 

 blood-vessels, which is pushed up into the lower end of the hair. 

 In consequence of the rich supply of food brought by these vessels 

 to the deep cells of the ectoderm lying above them, these cells 

 bud off horny cells with great rapidity and persistence, and in this 

 way a column of horny cells is formed which pushes out the older 

 part of the hair arid causes the whole structure to assume a great 

 length, sometimes equalling that of the body. The plug of dermis 



