292 



MANUAL OF HISTOLOGY. 



direction as the flat cells of the previous cuticula. Before the 

 internal root-sheath is pierced by the growing hair both cuti- 

 culffi are composed of similar cells. 



The root of the hair consists of cells closely resembling 

 those of the rete mucosum. The corpuscles seated directly 

 upon the basement-membrane of the papilla are cylindrical in 

 form, and the more superficial ones polyhedral. Near the hair- 

 shaft they are spindle-shaped and firmer. The lower cells of 

 the central part of the root of the hair are round, have a large 

 nucleus, and a small amount of cell-body. Afterward the cell- 

 body increases in size. They bear a close resemblance to em- 

 bryonic corpuscles and color deeply in carmine. In the upper 

 part of the root of the hair the cells of the external part of the 

 bulb become oblong, spindle-formed, and, finally, are lengthened 



out like fibres, in which condition they 

 form the fibrous part of the hair-shaft. 

 The pigment in the root of the hair is 

 sharply limited externally by the cells 

 of the hair-cuticula. 



The shaft of the hair consists of a 

 central part or medulla, and a fibrous 

 portion covered by the hair-cuticula. 

 The medulla consists of potyhedral 

 cells containing fat and pigment gran- 

 ules. Toward the free end of the hair 

 it becomes smaller, and finally ends 

 near the point. The fibrous portion 

 forms the principal part of the hair- 

 shaft, and consists of flattened, fusi- 

 form cells, containing numerous spin- 

 dle-shaped granules. 



From the foregoing description of 

 the hair and its follicle it is clear that 

 in transverse sections it will present 

 different appearances, according to the 



situation in which the section is made. A description of trans- 

 Terse sections in different regions of the hair is here unneces- 

 sary. We reproduce, however, above, a figure from Biesiadecki, 

 which will sufficiently explain this matter (Fig. 123). 



A hair increases in length by the formation of new elements 

 in its root, and they, by their subsequent elongation and move- 



PlO. 123. Transverse section of 

 the hair beneath the neck of the hair- 

 follicle : a, external sheath of the hair- 

 follicle ; 6, transversely cut blood-ves- 

 sels ; c. Inner sheath of hair-follicle ; 

 < basement-membrane of hair-follicle; 

 , cxtenwl root^sheath :/, cells of Ren- 

 te's layer ; g, cells of Huxley's layer ; 

 A, cuticnla ; I, hair-shaft. 



