STKUCTUEE OF HAIRS. 



695 



Fig. 308. 



Fio. 309. 



Fig. 310. 



intervals hj partitions that 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. The hairs 

 of the Bat tribe are commonly 

 distinguished by the projections 

 on their surface, which are 

 formed by extensions of the 

 component scales of the cortical 

 substance; these are particularly 

 well seen in the hairs of one of 

 the Indian species, which has a • 

 set of whorls of long narrow 

 leaflets (so to speak) arranged at 

 regular intervals on the stem 

 (c). In the hair of Pecari (Fig. 

 311), the cortical envelope sends 

 inwards a set of radial prolon- 

 gations, the interspaces of which 

 are occupied by the polygonal 

 cells of the medullary substance ; 

 and this, on a larger scale, is the 

 structure of the "quills" of the 

 Porcupine; the radiating parti- 

 tions of which, when seen through 

 the more transparent parts of the 

 cortical sheath, give to the sur- 

 face of the latter a fluted appear- 

 ance. The hair of the Ornitho- 

 rhyncus is a. very curious object; 



for whilst the lower part of it re- Pij. 309. Hair of Musk-deer, consisling almost 



semblesthefinehairofthemouse entirely of polygonal ceiu. 



1 j_i • j_i * 1 Fig. 310. A, Small Hair of Squirrel; b, Large 



or squirrel, this thms away and m^ of squirrel,- c, Hm? annatan Bat 

 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. 

 The structure of the Human hair is in certain respects peculiar. 

 "When its outer surface is examined, it 

 is seen to be traversed by irregular lines 

 (Fig. 312, a), which are most strongly 

 marked in foetal hairs ; and these are 

 the indications of the imbricated ar- 

 rangement of the flattened cells or scales 

 which form the cortical layer. This 

 layer, as is shown by transverse sections 

 (c, d), is a very thin and transparent cy- 

 linder; and it incloses the peculiar 



fibrous substance, that constitutes the principal part of the shaft 

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



Fig. 308. Hair of Suble, sbowiDg: large rounded*^ 

 cells in its interior, covered by imbricated scales 

 or flattened cells. 



Fig. 311. 



Transverse Section of Hair of 

 Pecari. 



