TACTILE SENSE. 



729 



extends a single nerve-fiber, which, penetrating the series of capsules, 

 terminates by sending its neuraxon into the central cavity of the cor- 

 puscle, at the top of which it ends in a simple extremity. Each cor- 

 puscle is covered with forty or fifty capsular layers. 



Krause's End-bulbs. The tactile corpuscles of Krause are elon- 

 gated, oval bodies, into one end of which a nerve-fiber penetrates. 

 Externally they have a covering of connective tissue, a continuation 

 of the perineurium, and an internal knob of granular matter dis- 

 posed in concentric layers with a few nuclei. In the center of this 

 knob is found the axis-cylinder which runs through it like a ribbon 

 to the upper pole and then ends in a slight thickening. These bulbs 



Fig. 297. Vater Pacinian Corpuscle from the Mesentery of the Cat, 

 Fixed in a Platinum Chlorid-osmic Acid Solution. X 45. (SOBOTTA.) 



The figure gives a general view of the corpuscle and not a cross-section. 

 a, Axis cylinder in the core, ik, Core, mn, Medullated nerve-fibers entering 

 the corpuscle. 



are found in the basement membrane of certain mucous membranes, 

 as in the corneal conjunctiva, in the mucous membrane of the mouth, 

 in the clitoris, and -in the glans penis. They are also to be found in 

 the skin. 



Corpuscles of Grandry or of Merkel consist qf two or more flat- 

 tened cells, each larger than a simple tactile cell. Each cell is 

 nucleated, and the nerve-fiber, before entering the corpuscle, loses 

 its white sheath, and the axis-cylinder ends as a flat disc lying 

 between the two tactile eel's. These tactile cells are piled one 

 upon the other so as to form a heap of cells. They are found chiefly 

 in the beak and tongue of the duck and in the epiderm of man. 



Other Modes of Ending. In addition to sensory nerves ending 

 by special structures as those just described, there are some which 



