STRUCTURE AND DEVELOPMENT OF HAIR. 



195 



composed of an assemblage of cells whose walls are flattened against 

 each other, as in a Vegetable pith; whHst the cortical envelope is 

 scarcely distinguishable. In the hair of the Mouse and other small 



Fig. 56. 



Structure of Hair : A, hair of Musk-deer, consisting almost entirely of polygonal cells; B, hair of Sable, 

 showing large rounded cells in its interior, covered by imbricated scales or flattened cells. 



Kodents, we see the horny tube crossed at intervals by partitions, which 

 are sometimes complete, sometimes only partial ; these are the walls of 

 the single or double line of cells, of which the medullary substance is 

 made up. 



329. In the Human hair, the representation of the cortical envelope 

 of the hair of other animals is found in a thin transparent horny film 

 which is composed of flattened cells or scales, arranged in an imbricated 

 manner, their edges forming delicate lines upon the surface of the hair, 

 which are sometimes transverse, sometimes oblique, and sometimes 

 apparently spiral (Fig. 5T, A). Within this, we find a cylinder of 

 fibrous texture, which forms the principal part of the shaft of the hair, 





Structure of the Human Hair : A, external surface of the shaft, showing the transverse stna> and jagged' 

 boundary, caused by the imbrications of the scaly cortex ; B, longitudinal section of the shaft, showing tt 

 fibrous character of the medullary substance, and the arrangement of the pigmentary matter; C, transverse 

 section, showing the distinction between the cortical and medullary substances and the central collection or 

 pigmentary matter ; D, similar transverse section without the dark centre. 



and it is in the centre alone, which is frequently more distinctly cellular, 

 that we find any close resemblance to the ordinary condition of the me- 

 dullary substance. The constituent fibres of the shaft are marked ^ out 

 by delicate longitudinal striae, which may be traced in vertical sections 

 of the hair (B) : but they may be still more completely demonstrated by 



