INTEGUMENT. 25 



ceous glands (Fig. 14, HBD], are. in connection with each hair-sac, 

 the latter serving to oil the hair. 1 



Sch 



FIG. 14. LONGITUDINAL SECTION THROUGH A HAIR. (Diagrammatic.) 



tie, stratum cornenm ; SM, stratum Malpighii ; Co, derma ; Ap, arrectores pili ; 

 Ft, adipose tissue ; F, outer longitudinal layer, and F 1 , inner transverse layer 

 of dermic coat (both composed of connective-tissue) ; Sck, hair-shaft ; M, 

 medulla ; E, cortex ; 0, cuticle of shaft ; WS, WS 1 , external and internal 

 root-sheath, the latter reaches above only as far as the point of entrance of 

 the ducts of the sebaceous glands (HBD] HP, hair-papilla, containing vessels ; 

 GH, hyaline layer, which lies between the inner and outer hair-sheaths, ie., 

 between the root-sheath and the follicle (dermic coat). 



As feathers are arranged, in definite tracts, so also hairs are 

 disposed more abundantly on some parts of the body than on others. 



1 The arrectores pili have also the function of compressing the glands, though the 

 latter are provided with muscles of their own, the development of which is in inverse 

 proportion to that of the proper hair-muscles. 



