30 



COMPARATIVE ANATOMY 



whether the old papilla remains, or whether a new one is formed. 

 The former method seems to occur in most instances, although not 



FIG. 23. LONGITUDINAL SECTION THROUGH A HAIR. (Diagrammatic.) 



Ap, arrectores pili ; Co, derm; F, outer longitudinal layer, and F ] , inner trans- 

 verse layer of connective tissue fibres of follicle ; Ft-, adipose tissue ; GH, 

 hyaline layer, which lies between the inner and outer hair-sheaths, i.e., 

 between the root-sheath and the follicle ; HBD, sebaceous glands ; HP, 

 hair-papilla, containing vessels ; M, medulla ; O, cuticle of shaft ; If, cortex ; 

 Sc, stratum corneum ; Sch, hair shaft ; SM, stratum Malpighii ; WS, WS 1 , 

 external and internal root-sheath the latter reaches above only as far as the 

 sebaceous ducts, and is not continuous with the epiderm. 



infrequently new hairs are formed throughout life direct from the 

 epiderm, as in the embryo. From a primary hair-germ an entire 

 group of hairs may be formed by subsequent division. 



The special tactile hairs (vibrissce, sinus-hairs) present on parts 



