272 



AN INTRODUCTION TO ZOOLOGY 



fibrillated cells, which in dark-coloured hair contain numerous 

 granules of a dense pigment. The outside is covered by a layer of 

 thin imbricated scales, the hair cuticle. At the bottom of the 

 follicle the hair expands to form a bulbous root, which is the actual 

 growing point and composed of soft protoplasmic cells. Into this 

 root fits a projection of the cutis termed the hair papilla, which is 

 plentifully supplied with blood-vessels. Often when the hair is 

 pulled out the epidemal portion of the follicle comes with it so that 

 it is sometimes termed the root sheath. Where the epidermis is 



-M 



Sb 



FIG. 87. Diagram of section of skin of mammal. 



C., corium or dermis ; E., epidermis ; F., fat ; F.L., fibrous layer ; H., hair follicle ; H.C., hair 

 cuticle ; M., medulla ; M.L., Malpighian layer ; P., hair papilla ; R., root sheath ; Sb., sebaceous 

 gland ; S.C., stratum coraeum ; S.D., duct of sweat gland ; Sg., sweat gland. 



turned in to form the follicle it is composed of two layers as on the 

 skin itself : the outer one corresponds with the stratum corneum, and 

 therefore comes to lie next to the hair itself, and is termed the inner 

 root sheath, being in itself composed of three layers of cells ; the 

 outer root sheath corresponds with the rete mucosum, and is con- 

 siderably thicker at the upper end, but thins off towards the base. 

 Outside these epidermal layers the cutis furnishes a hyaline layer in 

 the form of a fairly thick basement membrane, and around this again, 

 a layer composed of flattened fibres and cells circularly arranged. 

 The nerves of the corium penetrate the hyaline membrane and 

 arborise on the outside of the outer root sheath. In the vibrissae 



