THE RECEPTORS AND EFFECTORS 



81 



layer of the skin (dermis) in the lower part of the hair bulb, spreads out 

 over the inner hair follicle in a heavy plexus, and terminates chiefly in a 

 mantle of touch cells, resembling Merkel's corpuscles (see Fig. 26), in the 

 outer root sheath all over the follicle. A second nerve supply comes from 

 the dermal plexus of the skin, from which branches run down and form a 

 nerve ring about the neck of the follicle. Experimental studies show that 

 these hairs are very important not only as general tactile organs, but 



Fig. 23. Nerve-endings about a large hair from the dog. The nerve- 

 fibers are shown in black surrounding the hair shaft, the straight fibers 

 at b and the circular fibers at c. (After Bonnet, from Barker's Nervous 

 System.)~ 



specifically as aids in locomotion and equilibration. The ordinary hairs of 

 man and other mammals have three forms of specific nerve-endings in addi- 

 tion to various forms of terminal arborizations in the surrounding tissues: 

 (1) straight and often forked endings running parallel with the base of the 

 hair; (2) circular fibers forming a plexiform ring around the root of the 

 hair external to the straight endings; and (3) leaf -like nerve-endings associ- 

 ated with special cells resembling Merkel's corpuscles. Figure 23 illustrates 

 the first and second types of these endings. 



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