EXPLANATION OF THE PLATES. 



PLATE XXVIII. 



STRUCTURE OF HAIR. 



Fig. 1. shows the structure and depth of implantation of the 

 entire root of a hair of the scalp, magnified 130 

 diameters : it displays the two sheaths which in- 

 clude the stem, and its dilated extremity, the bulb, 

 and which is seen to rest upon a distinct cellular 

 vesicle ; the outer sheath completely surrounds the 

 base of the hair, and cuts it off from all direct 

 vascular supply ; the vessels, however, which 

 nourish the hair are seen to ramify on the external 

 surface of this sheath, which is also observed to be 

 surrounded by fat vesicles, the root having passed 

 through the thickness of the skin and imbedded 

 itself in the subcutaneous and fatty cellular tissue. 



Fig. 2. The root of a grey hair forcibly removed from the 

 scalp ; in this the outer sheath is seen to be broken 

 off just above the place at which the stem begins 

 to dilate into the bulb ; a similar rupture almost 

 invariably occurs in the outer sheath of all hairs, 

 whether coloured or uncoloured, which are forcibly 

 uprooted. The contrast between the coloured and 

 the uncoloured hair is striking. 



Fig. 3. The cells of which the outer sheath is composed : 

 magnified 670 diameters. 



Fig. 4. A portion of the inner sheath seen on its inner sur- 

 face, and magnified 350 diameters ; this is lined 

 with a layer of elongated and nucleated cells ; the 

 outer portion of this sheath is distinctly fibrous, the 

 fibres being formed out of the cells, the nuclei of 

 which become absorbed : the inner surface also ex- 

 hibits transverse markings, the impressions of the 

 scales of the stem of the hair. 



Fig. 5. Some of the pigment cells, of a multitude of which 

 the bulb of the hair is composed : magnified 670 

 diameters. 



