THE HAIRS. 



as these modified epithelial cells are called, possess fibrillae that pass between 

 adjacent cells similar to the intercellular bridges in the epidermis. A variable 

 amount of pigment, either diffuse, or as granules within or between the 

 spindles, is a constant constituent of the cortical substance. In blond hair 

 the color is chiefly diffuse, the pigment granules being often entirely want- 

 ing; in hair of darker shades, the granules predominate and increase in in- 

 tensity of color as well as in quantity. As the hair grows outwards from the 

 bulb, it loses much of its moisture, and in consequence later contains 

 minute air-vesicles that replace the fluid previously occupying the clefts 

 between the hair-spindles. 



The medulla, when well represented, is seen as an axial stripe, some- 

 what uneven in outline, that varies with illumination, with transmitted light 

 appearing as a dark band and with reflected light as a light one. This 

 peculiarity depends upon the presence of air imprisoned between the 

 shrunken and irregular medullary cells dried and cornified epithelial 

 elements which are connected by branching processes into a network in- 

 completely filling the medulla. The air within the shaft modifies the color 

 of the hair, since the resulting reflex tends to lessen the intensity of the tint 

 directly referable to the pigment. Even when conspicuous, the medulla 

 does not extend the entire length of the hair, often being interrupted and 

 always disappearing before reaching the tip. 



The Hair-Follicle. This structure includes: (i) a connective tissue 

 sheath, the theca, contributed by the corium; (2) an epithelial lining, the 



Outer root-sheath 



Hair surrounded by 

 inner root-sheath 





Adipose tissue 



Fibrous tissue 



FIG. 369. Horizontal section of scalp, showing group of transversely cut hair-follicles. X 65- 



outer root-sheath, continued from the deepest layer of the epidermis; and 

 (3) the inner root- sheath, an epithelial investment probably differentiated 

 within the follicle, and not a direct prolongation from the cuticle. 



The theca folliculi includes three strata: an outer, composed of 

 loosely disposed longitudinal bundles of fibrous tissue with a few cells and 

 elastic fibres; a middle one, made up of closely placed circular bundles; and 

 a very thin, homogeneous inner coat, the glassy membrane, which repre- 

 sents an unusually well developed basement membrane separating corium 



