390 



MANUAL OF HISTOLOGY. 



follicle, or bending off more at right angles, this cord pursues a downward 

 course to a greater or less distance, and eventually becomes continuous, 

 together with other of its companions, with a strong bundle of connective- 

 tissue down below. 



Rising from the fundus of this follicle, we next see the papilla of the 

 hair (i), consisting of a species of undeveloped nucleated connective-tissue 

 with a slight intermixture of fibres. This structure may be regarded as a 

 modified tactile papilla of the skin. Its shape is either conical or more 

 or less ovoid, the length from above downwards always exceeding the 

 breadth ; thus the former, foi instance, may amount to 0*2256 mm., and 

 the latter to 0*1128 mm. In. its interior is contained a fine capillary net- 

 work. This papilla is the point from which the hair is developed, and 



that also from whence the latter receives its 

 nutritive supply. 



a jgp^ ^e P resence of nerves, on the other hand, 



\ ^3 s^Z& l ias not been remarked in the papillae of hair, 

 7 /*jj%tfZ%/^^Eajffl although in man the external layer of the 

 ^ *** follicle contains isolated fibres, which are 



seen hero and there to undergo division. 

 According to recent observations, these latter 

 appear to be connected with peculiar terminal 

 cells situated in the external root-sheath, 

 which, as we have seen before ( 187), are 

 also to be found in the rete Malpighii of 

 the skin (Langerhans). 



213. 



The hair follicle being a portion of the 

 skin which has been folded in, as it were, 

 the external root-sheath (fig. 389, c; and 

 390, e,f) represents the undermost layer of 

 the rete Malpighii. As to the precise nature 

 of the internal root-sheath (fig. 389, d; and 



390, c, d), on the other hand, there still 

 exists considerable difference of opinion. 



If the entrance of the follicle be closely 

 examined, the deeper layers of cells of the 

 adjacent skin are seen descending as ex- 

 ternal root-sheath into the sac, and lining its 

 walls. The number of layers of these small 

 rounded and nucleated cells varies with the 

 strength of the hair (fig. 389, c; 390, e; and 



391, c). The cells themselves are about 

 0-0074-0 -01 13 mm. in diameter. Those of 

 the most internal stratum are more or less 

 flattened, while those situated more ex- 

 ternally appear to be elongated in a radial direction, recalling to mind 

 the state of things seen in the Malpighian layer of the skin. Just as 

 this outer root-sheath is continuous above with the rete mucosum, so is 

 it continued on reaching the fundus of the follicle (fig. 389, e) into the 

 cellular mass of the hair-bulb (h). In some cases, however, it does not 

 extend so far. 



The internal root-sheath is distinguished from the duller mass of the 



5 



Fig. 390. Transverse section of a 

 human hair from the head, with 

 its follicle, a, the hair; 6, cuticle of 

 the same; c, the inner, and d, the 

 outer layer of the so-called internal 

 root-sheath; , the external root- 

 sheath:; /, its peripheral portion 

 formed of elongated cells; g, hya- 

 line -membrane of the follicle ; h, 

 middle layer ; and t, external layer 

 of the latter. 



