SPECIAL END OKGANS. 



863 



ENDINGS OF NERVES OF GENERAL SENSATIONS. 



The peripheral endings of the nerves associated with the special senses have 

 been described in the preceding pages. Under this heading will be considered the 

 terminations of those sensory nerves which are widely distributed throughout the 

 body and are associated with the muscular sense and the senses of pressure, heat, 

 cold, and pain. These nerves may end as fine ramifications of the axis cylinders 

 lying free amongst the tissues, or in special end organs where the terminations of 

 the axis cylinders are surrounded by connective tissue capsules. 





FKEE NERVE-ENDINGS. 



Free nerve -endings are found chiefly in the epithelium covering the skin or 

 the mucous membranes. The nerve-fibres, after subdividing in the sub-epithelial 

 connective tissue, lose success- 

 ively their medullary and primi- c 

 tive sheaths and are continued 

 as naked axis cylinders, which, 

 if stained with gold chloride, are 

 seen to consist of fine varicose 

 filaments. The axis cylinders 

 subdivide and form primary and 

 secondary plexuses, and from 

 the latter numerous fibrillse 

 pierce the sub-epithelial base- 

 ment membrane and ramify be- 

 tween the overlying epithelial 

 cells where they end in minute 



knobs of flattened discs. In the Fia 739. VERTICAL SECTION OF CORNEA STAINED WITH 

 epidermis the nerve fibrillse are CHLORIDE OF GOLD (Ranvier). 



limited to the stratum mucosum, a> 6> primary plexus in connective tissue of cornea; Cj branch 



but in the cornea they reach the passing to sub-epithelial plexus e ; /, intra-epithelial plexus ; 



Surface layers of epithelium d > terminations of fibrils. 



(Fig. 739). Free nerve-endings 



also occur around the sudoriferous glands, in the papillae and root sheaths of the 



hair follicles, in the sub-epithelial and intermuscular connective tissues, and in 



serous membranes. 



i^^^> rf ^--.~:.-^>r\^v-^-^. S ;M,v.;v./ Modifications of free nerve-endings 



J are seen in the tactile discs or cells of 

 ::A-\ Merkel ; here the neuro-fibrillse end in 

 jy the deeper layers of the epidermis in 

 crescentic or cup-shaped expansions, in 

 contact with large, modified epithelial 

 cells. These tactile discs are well marked 

 in the pig's snout (Fig. 740). 



FIG. 740. ENDING OF NERVE IN TACTILE DISCS OF THE 



SNOUT (Ranvier). (From Quain's Anatomy. ) 



SPECIAL END ORGANS. 

 The special end organs vary greatly 



m ^ ZQ an( j fQ im> Du fc in all of them the ter- 



n, medullated fibre ; m, terminal discs in muscle ; e, m i na tion of the axis Cylinder is enclosed 



is applied. 



within aconnective tissuecapsuleorsheath 

 of varying thickness. The following are 

 the more important special end organs. 



(1) End Bulbs of Krause (Fig. 742). These are minute cylindrical or oval bodies 

 which are found in the conjunctiva, in the mucous membrane of the lips, and in 



