130 TRANSACTIONS, NATURAL HISTORY SOCIETY OK GLASGOW. 



With regard to the function of the layers, I may 

 add in conclusion that the two layers of the intei'- 

 nal root-sheath are for facilitating the outward 

 growth of the spine. The gliding takes place be- 

 tween Henle's layer and the internal cells of the 

 outer root-sheath. The external surface of Henle's 

 layer is always perfectly smooth, whereas frequently 

 on the internal surface the cells are seen interdigitat- 

 ing with those of Huxley's layer. 



