THE PERIPHERAL NERVE-ENDINGS. 



FIG. 99. 



CHAPTER VI. 



THE PERIPHERAL NERVE-ENDINGS. 



Terminations of Sensory Nerves. A medullated nerve, in 

 passing to its ultimate distribution, first loses the medullary sub- 

 stance, or white matter of Schwann, which ends abruptly at some 

 bifurcation of the nerve corresponding in position to a node of Ran- 

 vier. The fibre continues for a variable distance non-medullated, 

 being covered with the neuri- 

 lemma and the nerve-cor- 

 puscles ; these coats become 

 reduced gradually until the 

 neurilemma disappears, the 

 nerve-nuclei then alone re- 

 maining as an imperfect in- 

 vestment of the axis-cylinder. 

 The nuclei soon occur less 

 frequently, until finally they 

 disappear and the bundles of 

 nerve-fibrillae, by this time 

 greatly reduced owing to re- 

 peated division, continue as 

 naked axis-cylinders ; these 

 unite to form a widely-meshed 

 ground-plexus, possessing 

 characteristic triangular, nu- 

 cleated nodal points where 

 the bundles of fibrillae meet. 



The axis-cylinders sooner 

 or later break up into their 

 component primitive fibrillae, which unite with one another to 

 form rich net-works, or terminal plexuses, within the connective 

 tissue of the organ supplied ; in some instances these net-works are 

 situated immediately beneath the epithelium and represent the ulti- 

 mate distribution of the fibrillae ; in others, fine fibrillae emerge from 

 the plexus, enter the epithelium, and terminate in pointed or club- 

 shaped free endings between the epithelial cells. The nerves of 

 common sensation frequently end in this manner, including, probably, 

 many nerves of the skin, cornea, and mucous membranes. 



Many sensory nerves, however, terminate in special endings of 



Termination of sensory nerve fibres ; portion of the 

 plexuses occupying the anterior layers of the cornea ; 

 gold preparation : n, n, nodal points of the coarser 

 ground-plexus ; 6, small bundle of nerve- fibrils which 

 breaks up into the terminal plexus (ti of ultimate 

 fibrillae ; v, fibrils showing varicosities. 



