HAIR. 



[ 375 ] 



HAIR. 



or three layers of polygonal, longish, trans- 

 parent cells, with their long axis parallel to 

 that of the hair. The outermost (Ilenle's) 

 layer (figs. 299/, 301 A) consists of long, 



Fig. 301. 



mfmi 



n iilll 



J) 



\:f'^ 



Magnilicd 350 diameters. 

 Elements of the inner root-sheath. A, external layer : 

 1. isolated pirates ; 2, the same in connexion, showing 

 the int^^rspaces (a) between the cells (6). -B, cells of the 

 inner non-perforated layer. C, nucleated cells of the 

 lower part of the inner sheath, which consists of a single 

 layer only. 



flattened, non-nucleated cells, from 1-700 

 to l-oOO" in length, with fissures between 

 them, forming a fenestrated layer. The in- 

 nermost (Huxley's) layer (figs. 299 e, 301 B) 

 consists of one or two layers of shorter and 

 broader polygonal cells, from 1-1200 to 

 1-600" in length ; their nuclei, which exist 

 in the lower part only of the coat, are often 

 broader at the ends than in the middle, 

 sometimes curved and pointed. At the base 

 of the hair-foUicIe, the inner root-sheath 



consists of a single layer only of beautiful, 

 polygonal, nucleated cells (fig. 301 C) ; tliese 

 becoming soft, delicate and rounded, gra- 

 dually pass into the outer layers of the round 

 cells of the bulb. 



In regai'd to development, the rudiments 

 of the hair appear as processes of the rete 

 mucosum descending in the substance of 

 the cutis. These are solid, and consist of 

 cells, the internal of which become horny, 

 and form first a small slender hair in the 

 axis of the process, next an inner sheath 

 sm-rounding the former, whilst the outer 

 cells remain soft, and form the outer sheath 

 and the cells of the bulb. 



After birth the foetal hair appears to be 

 completely shed, new hairs being formed in 

 the old follicles, which displace the first set, 



as shown in figs. 302, 303. 

 Fig. 302. 



Fig. 303. 



Magnified 20 diameters. 

 Eye-lashes of a child a year old. A exhibits a process 

 (jn) of the bulb or outer root-sheath, in which the cen- 

 tral cells are elongated, and form a cone distinct from 

 the outer cells. -S, one more advanced, in which the 

 inner cone has become developed into a hair and an 

 inner root-?heath : a, outer, b, inner root-sheath of the 

 young hair; c, pit for the pulp; c?, bulb; e, shaft of the 

 old hair; f. bulb, .9, shaft, h, summit of the young hair; 

 i, sebaceous follicles ; k, three sudoriparous ducts open- 

 ing into the upper part of the hair-follicle. 



The hairs sometimes found developed 

 upon mucous membranes, and within en- 

 cysted tumours and ovarian cysts, possess 

 the normal structure in every respect. 



Of the morbid states of the human hair, 

 we need mention only the loss and change 



