1392 



HUMAN ANATOMY. 



Fig. 



The cuticle of the hair appears as a transparent outermost layer marked by a net-work of 

 fine sinuous lines, the irregular meshes of which have their longest diameter placed obliquely 

 transverse. These lines correspond to the free borders of extremely thin glassy cuticle-plates 



that overlie the hair as tiles on a roof, the imbrication involv- 

 ing from four to six layers. Seen in profile (Fig. 1155), the 

 contour of the hair-shaft, therefore, is not smooth but serrated, 

 the minute teeth formed by the free margins of the scales 

 being directed towards the tip of the hair. After isolation by 

 suitable reagents, the cuticular elements appear as transparent 

 structureless cells, quadrilateral in outline and curved to con- 

 form to the hair-shaft which they cover. 



The cortical substance, often indeed constituting practi- 

 cally the entire shaft, consists of elongated fusiform cells so 

 compactly arranged that the individual elements are only dis- 

 tinguishable after the action of disassociating reagents. In 

 addition to the remains of the shrunken nuclei the haij-- 

 spindles, as these modified epithelial cells are called, possess 

 fibrillse that pass between adjacent cells similar to the inter- 

 cellular bridges in the epidermis. A variable amount of 

 pigment, present either as a diffuse tint of the spindles, or as 

 granules within or between the same, is a constant constituent 

 of the cortical substance. In blond hair the color is chiefly 

 diffuse, the pigment granules being often entirely wanting ; in 

 hair of darker shades, the granules predominate and increase in intensity of color as well as 

 in quantity. As the hair grows outward 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. 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 medulla, when well represented, is seen as an axial stripe, somewhat 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 con- 

 nected by branching processes into a net-work incompletely filling the medulla. The air within 

 the shaft is a factor modifying the color of the hair, since the resulting reflex tends to lessen the 

 intensity of the tint directly 



Fig. 1156. 



-V ^ Outer loot sheath 



Portion of shaft of hair; A, shaft 

 covered with cuticle ; i, cuticle re- 

 moved to expose cortical substance ; 

 »«, medulla ,-125. a, A, isolated cells 

 of cuticle and of cortical substance 

 respectively. >, 240. 



Hair surrounded by 

 inner root-sheath 



Adipose tissue 



referable to the pigment ; 

 this diminution affects par- 

 ticulary the lighter shades, 

 as in dark hairs the large 

 amoufit of pigment masks 

 the reflex. 



The Hair-Folli- 

 cle. — This structure 

 consists essentially of 

 ( I ) a connective tissue 

 sheath, the theca, con- 

 tributed by the corium ; 

 (2) an epithelial lining, 

 the 07itcr 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 prolonga- 

 tion from the cuticle. 



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

 posed longitudinal bundles of fibrous tissue with few cells and elastic fibres ; a middle 

 one, made up of closely placed circular bundles ; and a very thin, homogeneous 

 inner coat, the glassy 7nembrane , which represents an unusually well developed 



Fibrous tissue 



Horizontal section of scalp, showing group of transversely cut 

 hair-follicles. >' 65. 



