184 SPECIAL HISTOLOGY. 



time at any rate, whilst the cells of the bulb are freed, and may be 

 pressed out of the sac. The papilla is ovate or fungiform, J-^o of a 

 line long, tT-sV of a line broad, and is connected with the layer of con- 

 nective tissue of the sac, by a pedicle ; it has sharp contours and a per- 

 fectly smooth surface, and in its structure completely agrees with the 

 papillae of the cutis, consisting of an indistinctly fibrous connective 

 tissue with scattered nuclei and fat granules, but not of cells. I have 

 taken every pains to discover vessels and nerves in the isolated papilla, 

 but in vain ; even acetic acid and dilute solution of caustic soda, which 

 in general do such excellent service in these cases, have failed, and 

 Hassall and Gunther met with the same results. It must not hence 

 be concluded, that ihepapilla contains no vessels or nerves, for we know 

 that in other places, where vessels do certainly exist, they often com- 

 pletely escape the eye ; as, for example, in the dermal papilla? and in 

 the villi; and with respect to the nerves, in the papillae of the cutis. 

 In some animals the vessels may very readily be seen. 



61. The root- sheath, or the epidermic investment of the hair-sac, is 

 continuous with the epidermis around the aperture of the follicle, and 

 may be divided into an external and an internal layer, which are dis- 

 tinctly defined from one another. 



The external root-sheath is the continuation of the stratum Malpigliii 

 of the epidermis, and lines the whole hair-sac, resting for its lower half 

 on the transparent membrane above described; higher up, when this 

 and the transverse fibres are absent, it lies directly upon the longitudi- 

 nally fibrous layer. Its structure corresponds exactly with that of the 

 stratum Malpighii, even in the having the outermost cells, which in the 

 negro, according to Krause, are always brown, and in whites are so, at 

 least in the hairs of the lalia majora, towards the upper part, arranged 

 perpendicularly. At the bottom of the hair-sac, the outer root-sheath, 

 its cells becoming gradually rounded, passes continuously, and without 

 any sharp line of demarcation, into the round cells of the hair-bulb which 

 cover the papilla. The outer root-sheath is generally about 3-5 times 

 as thick as the inner ; but not unfrequently it becomes thinned towards 

 its upper part, and below invariably passes into a very thin lamella. In 

 the coarse hairs it measures in the middle of the root 0-018-0-03 of a 

 line, and presents 5-12 layers of cells. 



The inner root-sheath (Fig. 68-e. g.) is a transparent membrane 

 which extends from almost the very bottom of the hair-sac, over more 

 than two-thirds of it, and then suddenly ceases. It is closely connected 

 externally with the outer root-sheath, internally with the cuticle of the 

 hair (its outer layer), so that normally there is no space between it arid 

 the hair; further it is distinguished by its great density and elasticity, 

 and it consists in all but its lowermost part, of two or even three layers 



