THE PERIPHERAL NERVE-ENDINGS. 



FIG. 102. 



Tactile corpuscles from the bill of duck : 

 A , simple, B, compound, corpuscle ; t, tactile 

 cells ; d, tactile disks ; n, medullated nerve- 

 fibres entering the nucleated capsules (s) into 

 which the neurilemma continues. 



FIG. 103. 



tactile corpuscles present increasing degrees of complexity of struct- 

 ure, the most highly specialized ending of this class being the tactile 

 corpuscle of Meissner, found in the 

 skin of the palmar surfaces of the 

 fingers and of the toes. 



The corpuscles of Meissner 

 are oval elliptical bodies, 45-140 ^ 

 long and 35-55 /* wide, situated 

 usually at the apices of the papillae 

 of the corium ; they possess nu- 

 merous transversely-placed nuclei, 

 which, with the edges of the indis- 

 tinctly defined tactile cells, produce 

 the characteristic transverse or some- 

 what spiral markings. Each cor- 

 puscle is supplied with one or two, 



sometimes three or four, medullated nerve-fibres, which are invested 

 with Henle's sheaths; the fibres may undergo numerous windings 

 before entering the corpuscle, the sheath of Henle, together with 

 the neurilemma, becoming continuous with the 

 fibrous envelope of the corpuscle. The nerve- 

 fibres retain their medullary substance for a short 

 distance, but later lose this sheath and break up 

 into a number of non-medullated fibres ; these 

 latter subdivide into fibrillae, which pursue a spiral 

 course throughout the corpuscle, being connected 

 here and there with terminal disks. The com- 

 pressed tactile cells themselves are usually indis- 

 tinctly defined, the transversely-placed nuclei and 

 the outlines of the cells producing the transverse 

 markings. A large number of the nuclei seen, 

 however, belong to the superficial layers con- 

 tributed by the connective-tissue coverings. As 

 to the exact course and mode of termination of 

 the nerve-fibrillae within these tactile corpuscles, 

 much uncertainty still exists. 



The spherical end-bulbs of the conjunctiva 

 and of other mucous membranes, as well as the 

 genital and the articular nerve-corpuscles, 

 must be included in this class of nerve-endings ; 

 these bodies are all formed on the same general plan, the differences 

 in their structure being limited to the details of arrangement. 



The End-Bulbs. The third group of special nerve-terminations 

 embraces the nerve-endings of a cylindrical type in contrast to the 



Tactile corpuscle of 

 Meissner from the skin of 

 human toe : jV, the nerve 

 entering the complicated 

 group of tactile cells com- 

 posing the corpuscle ; Bl, 

 blood-vessel accompany- 

 ing the nerve-fibre. (After 

 Schieffer decker.*) 



