THE HAIR 285 



membrane is highly refractive and contains very few connective tissue 

 cells or fibers. 



The circular filters of the dermal root sheath contain interlacing 

 bundles of connective tissue fibers, which are mostly disposed in a ring- 

 like manner. Elastic fibers are absent. Within this layer is a dense 

 anastomosing plexus of capillary blood-vessels, together with a rich 

 subepithelial plexus of non-medullated nerve fibers. 



The longitudinal filters of the connective tissue root sheath also form 

 interlacing fiber bundles, most of which are somewhat obliquely disposed. 

 The bundles are coarser than those of the preceding layer and contain 

 a few elastic fibers. This portion of the root sheath contains many small 

 blood-vessels and nerves which supply the plexuses of the circular layer. 



The hair follicle in transverse section varies in different races from 

 circular to elliptical form. In the Chinese race the diameter of the fol- 

 licle and the hair is 100 X 7? to 85, in the European 100 X 62 to 72, 

 and in the Negro 100 X 40 to 60. The more elliptical the form of the 

 follicle the greater the curl of the hair. 



ATYPICAL PORTIONS or THE HAIR FOLLICLE. As already indicated, 

 the hair follicle presents some structural differences at various levels. 

 The typical arrangement is found only in the mid-portion of the fol- 

 licle. 



In its superficial portion the hair lies free in the follicular lumen, 

 the interval between it and the inner root sheath being only partially 

 occupied by the fatty secretion of the sebaceous gland which enters the 

 lumen of the follicle at the deeper portion of its middle segment. At 

 this level also, the root sheaths of the hair offer a gradual transition 

 from their typical structure to that of the dermal and epidermal layers 

 with which they are continuous. 



The hair bulb likewise differs prominently from the typical struc- 

 ture of the hair root. In this portion the germinal layers are very 

 highly developed at the expense of the horny layers. It is, therefore, 

 in this portion that growth is most active. The cells of this region are 

 often deeply pigmented. The increased size of the germinal layer, more- 

 over, produces a distinct bulging of the follicle, which incloses the hair 

 papilla and results in the peculiar bulbous shape of the extremity of the 

 hair follicle. 



THE HAIR PAPILLA. The structure of the hair papilla is identical 

 with that of the vascular papillae of the derma except that it is con- 

 structed upon a much larger scale. It consists of a conical or club- 

 shaped elevation of connective tissue which indents the extremity of 



