418 



INNERVATION. 



[CHAP. xiv. 



Fig. 87. 



appears here and there to be tubular, e. The shaft is much 

 narrower than the bulb, and is produced by the rather abrupt 



condensation and elongation into hard 

 fibres of the cells, both of those which 

 contain pigment and those which do 

 not. These fibres may be demon- 

 strated by simply crushing small frag- 

 ments of hair, but they become more 

 conspicuous when the tissue is softened 

 by a strong acid. The granules of pig- 

 ment assume a linear arrangement be- 

 tween the fibres, which are firmly united 

 into a solid rod by a material similar, 

 it may be supposed, to that which 

 cements the scales of the cuticle. 



The central series of cells just men- 

 tioned, when filled with pigment, seems 

 less disposed to become fibrous than those 

 around ; and some authors have described 

 Buib of a smaii black hair, from the jt as a medulla, in distinction from the 



scrotum, seen in section, a. Basement 1-11 JT 



membrane of the foilicle. b. Layer of fibrOUS part Ol the shatt. whlCQ tlievthen 

 epidermic cells resting upon it, and be- 



coming more scaly as they approach c, term COTtCX. J3ut the tubular Character, 

 a layer of imbricated cells, forming the . 



outer lamina, or cortex, of the hair, however constant in the hair or many 



These imbricated cells are seen more . . . . 



flattened and compressed, the higher animals, is very variable in human hair, 



they are traced on the bulb. Within , ,.. ., , -i ,! 



the cortex is the propsr substance of both in different situations, and in the 



the hair, consisting at the base, where . , T/W * *. i ^.i. 



it rests on the basement membrane, of samehair at ClllierentpOmtS Ol its length, 



small angular cells scarcely larger than n i n 



their nuclei. At d, these cells are more as may be SCCU VCry Well by means Ol 



bulky, and the bulb consequently thick- . . _ , x 



er; there is also pigment developed trailSVerSC SCCtlOnS (fig. OO, , 0)."* 



in many of them more or less abun- i i i i 



dantiy. Above d, they assume a de~ The human hair has a proper bark, 



cidedly fibrous character, and become -. . ., /,-,-, 



condensed, e. A mass of cells in the or cortex, formed in the following way. 



axis of the hair, much loaded with pig- ii /JT n J .. i 



ment. A single layer of the cells immediately 



surrounding those about to form the fibrous tissue of the shaft are 

 seen near the bottom of the follicle to assume an imbricated arrange- 



* Transverse sections of extreme thinness may be made by fixing a lock of 

 hair between two pieces of card or wood in a vice, and then shaving it with a 

 razor. In many animals, as the horse and dog, the hairs are tubular. In others 

 they present a central series of cells, round or compressed, with or without 

 pigment, as in the cat and mouse. In others again, their external surface is 

 regularly marked by annular, and sometimes toothed projections, as in the 

 Indian bat : and numerous other varieties might be enumerated. The quills 

 of the porcupine, and the feathers of birds, are modifications of the epidermic 

 tissue, and, in their essential characters, are closely allied to hairs. See Busk, 

 in Microsc. Journal. 



