1030 



VERTEBRATED ANIMALS 



sometimes be distinctly made out to consist of flattened scales 

 arranged in an imbricated manner, as in some of the hairs of the 

 sable (fig. 760) ; whilst in the same hairs, the medullary substance 

 is composed of large spheroidal cells. In the musk deer, on the 

 other hand, the cortical substance is nearly undistinguishable, and 



FIG. 760. Hair of sable, showing large 

 rounded cells in its interior, covered 

 by imbricated scales or flattened cells. 



FIG. 761. Hair of musk-deer, consist- 

 ing almost entirely of polygonal cells. 



almost the entire hair seems made up of thin -walled polygonal cells 

 (fig. 761). The hair of the reindeer, though much larger, has a very 

 similar structure ; and its cells, except near the root, are occupied 

 with hair alone, so as to seem black by transmitted light, except 

 when penetrated by the fluid in which they are mounted. In the 

 hair of the mouse, squirrel, and other small rodents (fig. 762, A, B), 



the cortical substance forms a 

 tube, which we see crossed at 

 intervals by 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 its stem (C). In the hair of the peccary (fig. 763) 

 the cortical envelope sends inwards a set of radial prolongations, the 

 interspaces of which are occupied by the polygonal cells of the medul- 

 lary substance ; and this, on a larger scale, is the structure of the 

 ' quills ' of the porcupine, the radiating partitions of which, when seen 

 through the more transparent parts of the cortical sheath, give to 



FIG. 762. A, small hair of squirrel ; B, large 

 hair of squirrel ; C, hair of Indian bat. 



