542 



THE MICROSCOPE. 



Hairs. The form and structure of these differ much; 



some are cylindrical, others flattened. A hair is divided 

 into a body or shaft, and a root which 

 is in the skin. (Fig. 276.) The shaft 

 is again divided into two parts : the 

 external is termed the cortical portion, 

 and the internal the medullary portion; 

 the latter does not usually exist in the 

 whole length of the shaft. The cor- 

 tical part consists of fibres, arranged 

 parallel to each other : besides these 

 there are, on the exterior, minute scales, 

 like epithelium, which are arranged 

 like the tiles on a house, and produce 

 the appearance of transverse markings. 

 The fibres gradually expand out, form- 

 ing a wall to the bulb enclosed in its 

 capsule. The development of a hair 

 commences at the bottom of the fol- 

 licle, and by the aggregation of suc- 

 cessive cytoblasts, or new cells, is 

 gradually protruded from the follicle, 

 both by the elongation of its consti- 

 tuent cells, and by the addition of new 

 layers of these to its base; the apex 

 and shaft of hair being formed before 



Fig. 276. A single Hair, the bulb, just as the crown of a 



een near its bulb. ^^ ^ ^ Q ^ Q ^ fang> The cyt() . 



blasts are round and loose at the base of the hair, bufc 

 are more compressed and elongated in the shaft ; and 



7, Transverse section of human hair, showing the cylinder of medullary sub- 

 stance. 2, Longitudinal section, showing the fibrous character of the same 

 pigment or colouring matter, and serrated edges. 



by this rectilinear arrangement the hair assumes a fibrous 

 character. Of sixteen species of the Bat tribe, the hairs of 



