THE SKIN. 289 



ing largest at its lower end, where it rests upon the papilla. 

 Below the neck we have the follicle and the root of the hair. 



The follicle consists, anatomically, of three layers : the ex- 

 ternal, middle, and internal hair-follicle sheaths. 



The external sheath of the follicle (d) consists of connective- 

 tissue fibres, which extend from the upper corium and running 

 parallel to the long axis of the hair-follicle surround the base 

 of the latter and send some fibres into the papilla. The fibres 

 forming the inner portion of this sheath are arranged much 

 more closely than the fibres forming the external part. In this 

 latter situation there is no sharp dividing line between the 

 sheath and the surrounding loose connective tissue, the one 

 merging gradually into the other. Within this sheath run the 

 special blood-vessels and nerves of the hair-follicle. 



The middle sheath of the follicle consists of a few transverse- 

 ly running connective-tissue fibres, between which lie oval nuclei 

 imbedded in a granular substance. Tliese latter, probably, 

 represent organic muscle-cells. This sheath begins at the neck 

 of the follicle and, surrounding its lower part, passes also within 

 the papilla. In this tissue is a close network of blood-capil- 

 laries. Nerves have not as yet been observed, though they 

 probably exist. 



The internal sheath of the follicle is composed of a trans- 

 parent, homogeneous-looking structure the basement-mem- 

 brane, which is riot altered by the action of acids or alkalies. 

 It is merely a continuation of the transparent membrane found 

 between the rete mucosurn and the corium, which it resembles 

 in its structure. It contains neither blood-vessels nor nerves. 

 The external surface is smooth, but the internal surface has a 

 notched appearance, caused by prolongations inward between 

 the cells of the external root-sheath of the hair. 



The hair -papilla is formed from the stroma of the hair-fol- 

 licle sheaths, especially from that of the middle sheath. It 

 consists of connective-tissue fibres, between which are found 

 numerous round cells. The internal follicle sheath separates 

 it from the root of the hair. Within the papilla are found 

 one or more arteries and veins besides non-medullated nerve- 

 fibres. The papilla has a narrow neck, a thicker body, and 

 a conical apex. It is, on an average, twice as long as it is 

 broad. The breadth is in direct proportion to the length of 

 the hair. 



