258 



THE TISSUES. 



layer of the hair-sac, except on the lower half of the sac. At the 

 bottom of the latter, the cells of this layer pass gradually into the 

 round cells which cover the papilla. It is generally three to five 

 times as thick as the inner layer; containing from five to twelve 

 layers of cells, and terminating below in a very thin lamella. 



The inner root-sheath (Fig. 162, e,f) is a transparent membrane, 

 extending from the bottom of the hair-sac over more than two- 

 thirds of it. It is connected externally with the external layer just 

 described (g), and internally with the cuticle of the hair; being, in 

 fact, blended with the latter (c, d). It is very dense and elastic, and 

 consists, except in its lowermost part, of two or three layers of poly- 

 gonal, elongated, transparent, and somewhat yellowish cells, with 

 their longitudinal axes parallel to that of the hair. The cells form- 

 ing the outermost layer of the two (or three), and which alone was 

 formerly known, are elongated and without nuclei. Those of the 

 innermost layer (Huxley's layer) are also polygonal, but shorter 

 and broader, and always (in the lower half, at least, of the root- 

 Fig. 165. 



Cells, &c., of inuer root-sheath. A. From its outer layer: 1, its isolated plates; 2, the same in 

 connection after the action of caustic soda ; a, apertures between the cells &. B. Cells from the inner 

 layer, with elongated and slightly notched nuclei, c. Nucleated cells of the lowest part (single 

 layer) of the inner sheath. Magnified 330 diameters. (KUlliker.) 



sheath) possessed of distinct elongated nuclei. (Fig. 165.) This 

 layer, however, also blends with the cells of the hair-bulb, like the 

 exterior. (Fig. 162, m.) 



Finally, the papilla of the hair (I) belongs to the sac, and corre- 



