706 



STRUCTUEE OF HUMAN HAIR. 



Fig. 367, 



Ornithorhyncus is a very curious object; for whilst the lower part 

 of it resembles the fine hair of the Mouse or Squirrel, this thins 



away and then dilates again into 

 a very thick fibre, having a 

 central portion composed of 

 polygonal cells, enclosed in a 

 flattened sheath of a brown 

 fibrous substance. 



552. The structure of the 

 Human Hair is in certain re- 

 spects peculiar. When its outer 

 surface is examined, it is seen 

 to be traversed by irregular lines 

 (Fig. 368, a), which are most 

 strongly marked in foetal hairs ; and these are the indications of the 

 imbricated arrangement of the flattened cells or scales which form 



Transverse section of Hair of 

 Pecari. 



A. 



i.ir»-' •■■!■:'-- -"•"r"3 



\l 



* **&m 



Hii' 





Structure of Human Hair : — a, external surface of the shaft, 

 showing the transverse striaj and jagged boundary caused by the 

 imbrications of the Cortical substance ; b, longitudinal section 

 of the shaft, showing the fibrous character of the Medullary 

 substance, and the arrangement of the pigmentary matter : 

 c, transverse section, showing the distinction between the trans- 

 parent envelope, the cylinder of medullary substance, and the 

 cellular centre ; d, another transverse section showing deficiency 

 of the central cellular substance. 



the Cortical layer. This layer, as is shown by transverse sections 

 (c, d), is a very thin and transparent cylinder ; and it encloses the 

 peculiar fibrous substance that constitutes the principal part of 

 the shaft of the hair. The constituent fibres of this substance, 

 which are marked-out by the delicate striae that may be traced in 

 longitudinal sections of the hair (b), may be separated from each 

 other by crushing the hair, especially after it has been macerated 

 for some time in sulphuric acid; and each of them, when com- 



