124: EXCRETION. 



inelastic fibres arranged for the most part longitudinally, 

 provided with blood-vessels and a few nerves, containing 

 some fibro-plastic elements, but deprived entirely of elastic 

 tissue. This is the thickest of the three membranes and is 

 closely connected with the corium. Next to this is a fibrous 

 membrane composed of fusiform, nucleated fibres arranged 

 transversely. These resemble the organic muscular fibres, 

 but are believed by Kolliker to be fibres of connective tis- 

 sue. 1 The internal membrane is structureless, and corre- 

 sponds to the amorphous layer of the true skin. The papilla 

 at the bottom of the hair-sac varies in size with the size of 

 the hairs, and is connected with the fibrous layers of the 

 walls of the follicle. It is composed of amorphous matter 

 with a few granules and nuclei, and probably contains blood- 

 vessels and nerves, though these are not very distinct. 



Although these different membranes are sufficiently recog- 

 nizable, it is evident that the hair-sac is nothing more than 

 an inversion of the corium, with some slight modifications in 

 the character and arrangement of its anatomical elements. 

 The fibrous membranes correspond to the deeper layers of 

 the true skin, w r anting the elastic elements, and presenting a 

 peculiar arrangement of its inelastic fibres, the external 

 fibres being longitudinal and the internal fibres transverse. 

 The structureless membrane corresponds to the upper layers 

 of the true skin, which are composed chiefly of amorphous 

 matter. The hair-papilla corresponds to the papillae on the 

 general surface of the corium. 



The investment of the root of the hair presents two dis- 

 tinct layers. The external root-sheath is three or four times 

 as thick as the inner membrane, and corresponds exactly with 

 the Malpighian layer of the epidermis. This sheath is con- 

 tinuous with the bulb of the hair. The internal root-sheath 

 is a transparent membrane, composed of flattened cells, 

 mostly without nuclei. This extends from the bottom of the 

 hair-follicle, and covers the lower two-thirds of the root. 



1 KOLLIKER, Handbuch der Gewe belehre des Menscken, Leipzig, 1867, S. 132. 



